geology and estimation of high grade zone at red lake mine

The Geological Setting and Estimation of Gold Grade of the High-grade Zone,Red Lake Mine, Goldcorp Inc.

TIM TWOMEY and STEPHEN McGIBBONRed Lake Mine, Goldcorp Inc.

Balmertown, Ontario, Canada, P0V 1C0

Received April 15, 2002; accepted September 25, 2002.

Abstract — The High-grade Zone (HGZ) was discovered 5000 ft (1520 m) below surface in thehangingwall of the existing orebody, 46 years after the Red Lake mine first went into production.The very rich ore of the HGZ is characterized by a remarkably abundant distribution of visible nativegold. The location of this discovery challenged conventional wisdom at the time and its genesis hasyet to be fully understood. Textural observations of ore within carbonate veins as well as crosscut-ting relationships suggest peak-metamorphic emplacement for at least some of the gold. Post-lam-prophyre dike remobilization of gold is locally observed in the HGZ. Structure and dilatancy werethe key elements for localizing ore at the Red Lake mine. Ore occurs where a fault trend intersectedfolded ultramafic volcanic rock that created a semi-permeable cap-rock to ore fluids ascending the“feeder” structure. This was enhanced by strong competency contrasts between the eastern ultra-mafic rocks, felsic volcanic rocks west of the HGZ, and the mafic volcanic host to ore – an excep-tional environment for the development of protracted dilatant fluid pathways for gold deposition.

Development in the HGZ began in February 2000 and reached commercial production on Janu-ary 1, 2001 at a capital cost of US $53 million. December 2001 reserves are 1.9 million short tons(1.73 Mt) at an average cut and diluted grade of 2.05 ounces per ton gold (70.5 g/t) containing 3.8million ounces of gold. The extremely rich ore presented a unique challenge in grade estimation forthe Geology Department at the mine. The historic cutting factor was replaced by a statistical methodas more data were collected from mining and mill reconciliation. The mine produced 503 000 ouncesof gold in 2001. Exploration at the mine is targeting HGZ-type ore formation within basalts associ-ated with the intersections of fluid pathways and folded ultramafic rocks, as well as other targets.© 2002 Canadian Institute of Mining, Metallurgy and Petroleum. All rights reserved.

Introduction

The Red Lake mine is located in the historic Red Lakegold camp of northwestern Ontario. High grades and com-plex geometry characterize the ore that has been mined fromthis district. Approximately 20 million ounces of gold have been mined to the end of 2001 (http://www.mndm.gov.on.ca/MNDM/MINES/resgeol/redlkprode.htm),primarily from rocks within the upper stratigraphy of theBalmer assemblage.

Gold was first mined in the camp in 1930, and of the 18historic producers, only two are operating today. PlacerDome’s Campbell mine and Goldcorp’s Red Lake mine arethe top two producers in the camp both by number of ouncesand average reserve grade. The two mine properties are con-tiguous and share a large hydrothermal system comprising anumber of individual ore zones. The orebody at the Camp-bell mine and the Red Lake mine is prolific, having a com-bined total resource (i.e., ounces mined and ounces inreserves and resources) equaling 23.5 million ounces of goldat an average grade of 0.65 ounces per ton (oz/t) gold or 22.3grams per tonne (g/t).

The Red Lake mine property consists of 58 patentedclaims in Balmer Township. These include the claims origi-

nally held by Dickenson Mines (Goldcorp’s predecessor) aswell as the claims obtained from Detta, ConsolidatedBrewis, and Robin Red Lake. Dickenson went into produc-tion in 1948, beginning on the same narrow veins thatcrossed the Campbell boundary to the west and averaged0.50 oz/t (17.0 g/t) across a 5 ft (1.5 m) mining width. Dur-ing the next 48 years, mining progressed to depth and to thesoutheast away from the Campbell mine. By 1970, the orecharacter underwent a transition to lower-grade dissemi-nated sulfide ore with a head grade of 0.30 oz/t (10 g/t). Asmining progressed further away from No. 1 Shaft withdepth, a winze called No. 2 Shaft was sunk in 1970 from the23rd level at 3400 ft (1040 m) below surface. No. 2 Shaftextends to the 38th level at 5600 ft (1700 m) below surface.The 38 levels in the mine are roughly 150 ft (46 m) apart.Total production to 1996 at the Red Lake mine was 3.2 mil-lion ounces of gold. Mining was suspended in 1996 to 2000as a result of a four-year labor dispute.

History of the HGZ Discovery and Development

The first drill hole to intersect the HGZ was a 150 ftlong, flat hole drilled in 1987 from the 30th level, the bot-

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Explor. Mining Geol., Vol. 10, Nos. 1 and 2, pp. 19–34, 2001© 2002 Canadian Institute of Mining, Metallurgy and Petroleum.

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Fig. 1. Photo of extreme high-grade gold specimen, taken from theMain zone of the HGZ, first cut in 32-826-1 Stope, in December2000. Central vertical band is composed of about 70% native gold,surrounded by disseminated flakes of gold as well as flat fracturesplated with gold on left side of photo. This museum quality speci-men contains approximately 300 oz of gold equivalent to 7284.0 ozper ton or 3.6 oz per pound. Hand lens is 2 in. (6 cm) long.

tom working level of the Red Lake mine at that time. Hole30L387 was drilled into the hangingwall of the mine inthe opposite direction from the known orebody at thattime, the lower-grade sulfide ore. The hole intersected oregrading 1.71 oz/t (58.6 g/t) across 19.1 ft (5.8 m) and con-tained numerous flecks of visible gold in a quartz-carbon-ate vein structure. This was recognized as typical “Camp-bell-type” high-grade ore. A small cut-and-fill stope wasdeveloped and mined up only half a level until it wasexhausted by the early 1990s. Systematic explorationbelow this elevation was delayed until 1991 due to a short-age of capital.

Long, flat exploration holes drilled from the 34th levelshaft station, 5000 ft (1520 m) below surface, were com-pleted in 1991. These results gave Goldcorp Inc. sufficientencouragement to finally embark on a follow-up program inlate 1994. The program was successful and Goldcorp recog-nized the significance of this distinctive ore as being similarto the ore intersected in hole 30L387. The 1994 drill cam-paign is considered to have been responsible for the discov-ery of the HGZ as its size was just beginning to be appreci-ated. In February 1995, Goldcorp announced a two-yearexploration and development program for the Red Lakemine. The first press release on the HGZ on March 29, 1995,stated that a “significant reserve expansion” was suggestedby exploration drilling on the 34th level in which “theweighted average grade for nine reported drill intersectionswas 9.08 oz/t gold, uncut, over 7.6 ft” or 311 g/t over 2.3 m.Goldcorp Inc.’s stock doubled in price within weeks of thatpress release.

Diamond drilling intensified on the discovery below the30th level, within a block of ground extending to 6200 ft(1890 m) below surface. Delineation of the HGZ orebodyidentified a series of zones, one of which is part of the ear-lier mined-out stope on the 30th level. In all, 27 sub-zonesmake up the HGZ between Footwall 4 (FW4) in the footwallto the Hanging Wall 5 sub-zone (HW5), furthest into thehangingwall to the southwest. Audited reserves for the HGZin 1999 reported 1.7 million tons at an average cut anddiluted grade of 1.37 oz/t gold. Development was started inMarch 2000 and production began at the end of 2000 with acapital cost of US$56 million. Audited reserves to Decem-ber 2001 on the HGZ have increased to 3.80 million ouncesin 1.85 million tons at an average cut and diluted grade of2.05 oz/t (70.3 g/t) gold (February 7, 2002, Goldcorp Inc.news release).

The HGZ discovery took place 5000 ft (1530 m) belowsurface and in the hangingwall of the original ore zones 48years after the mine first came into production. A remark-able characteristic of this ore is the abundant distribution ofvisible native gold and the attendant high grades (Fig. 1).The location of this discovery challenged conventional wis-dom at the time, which had suggested a limited potential forhigh-grade veins at depth to the east. Interestingly, the No. 2Shaft was deepened in 1978 to the 38th level even though noore was then outlined in the mine below the 28th level. This

initial “leap of faith” is now hoisting better than 2.00 oz/t orefrom the HGZ.

Development and Mining

Development within the HGZ began in February2000 and by year-end, approximately 92 800 tons of orehad been mined. Some 35% more ounces were minedthan predicted by the ore reserve. Commercial produc-tion began January 1, 2001 and for the year endingDecember 31, 2001 (see Fig. 2), a total of 246 618 tonsof ore was processed at a grade of 2.26 oz/t (77.5 g/t) fora total gold content of 535 000 ounces excluding con-centrates (February 7, 2002, Goldcorp Inc. newsrelease). The tons of ore extracted were also slightlyhigher as compared to ore reserves as some material atthe margins of stopes often proved to be economic. Totaldilution of 33% was comparable to the ore reserve esti-mate. Part of the Red Lake mine ore is refractory due tothe presence of gold-bearing arsenopyrite. The conven-tional mill (gravity and cyanide) liberates 88% of thegold and produces a sulfide concentrate currently being

20 Explor. Mining Geol., Vol. 10, Nos. 1 and 2, 2001

resent magmatic and erosional events that occurred over aperiod of approximately 290 million years (Stott and Corfu,1991; Sanborn-Barrie et al., 2000, 2001).

The belt is subdivided into several distinct assemblages.The Balmer assemblage, which hosts the Red Lake mine, ispart of the oldest Lower Mafic Sequence that constitutes50% of the Red Lake greenstone belt and forms its centralcore. The assemblage consists primarily of basaltic tholeiiteand komatiite lava flows, ranging in age from 2992 Ma to2958 Ma (Stott and Corfu, 1991). Gold in the Red Lake beltis predominantly associated with the upper part of theBalmer assemblage. Interestingly, almost all the gold pro-duction (98%) in the Red Lake greenstone belt has comefrom the southeastern half of the belt, even though favorablerocks, alteration, and structure are found throughout theentire belt.

The Balmer assemblage is unconformably overlain bythe Bruce Channel assemblage, which is dominated bymetasedimentary rocks and is folded around the Balmerassemblage to the southeast of the Red Lake mine. Some ofthese rocks are re-interpreted as the new Huston assemblage(Sanborn-Barrie et al., 2001). The unconformity with theunderlying Balmer assemblage is exposed on Highway 125near the Balmertown cemetery (O’Dea, 1999). Other assem-blages are discussed in more detail in Sanborn-Barrie et al.(2000, 2001).

The supracrustal rocks have undergone greenschist meta-morphism, and an amphibolite facies isograd occurs as a con-tact aureole around the belt-edge batholiths and bisects the

trucked to an outside facility for further processing.Overall gold recovery is approaching 96%.

Regional Geology

The Red Lake greenstone belt is situated in the westernportion of the Uchi Subprovince, a typical Archean granite-greenstone terrain consisting of volcanic and sedimentaryassemblages and synvolcanic intrusions (Fig. 3). These rep-

The Geological Setting and Estimation of Gold Grade of the High-grade Zone, Red Lake Mine • T. TWOMEY AND S. MCGIBBON 21

Fig. 2. A 3D view of HGZ reserves and resources and mine work-ings, looking north. Red areas show where mining of HGZ ore hastaken place to the end of 2001.

Fig. 3. Geology of the Red Lake greenstone belt (modified from Sanborn-Barrie et al., 2001).

Red Lake mine property (Andrews et al., 1986). Rocks of theregion have been subjected to at least two phases of deforma-tion (Sanborn-Barrie et al., 2001). The first episode, (D1), wasresponsible for the development of large-scale, northeast-trending folds. For example, northeast-trending synclines andanticlines occur northeast of McKenzie Island to the west ofEast Bay. On the eastern side of East Bay, a major fold with anorthwest-trending fold axis occurs in Bateman and Balmertownships. The second episode, (D2), corresponds to a north-east-southwest compression responsible for the developmentof a penetrative, southeast-trending schistosity, (S2), that isaxial planar to steeply east-plunging F2 folds.

Gold deposits in Red Lake are hosted within stronglyaltered and variably deformed rocks that are arranged alongregional trends (Andrews et al., 1986). Rocks from theCampbell and Red Lake mines occur within a 3⁄4 mile-widegeochemical anomaly whose presence is based on elevatedperaluminosity index, and arsenic and CO2 contents(MacGeehan et al., 1982). This is part of an alteration/defor-mation trend that extends to the northwest of the Red Lakemine and encompasses the past producing Cochenour-Willans mine (1.2 million oz) and the past producing

McKenzie mine (650 000 oz). This corridor has been calledthe Cochenour-Gullrock Deformation-Alteration Zone andits formation remains unresolved (Durocher, 1983; Andrewset al., 1986; Zhang, et al., 1997). The four largest mines inthe Red Lake camp including the Campbell, Red Lake,Madsen and Cochenour-Willans mines, display an unusualtype of alteration that is found in Balmer assemblage basaltsconsisting of so-called “aluminous bleaching.” This distinc-tive, buff-colored silicification represents the product ofintense cation leaching of K, Na, Ca, Fe, Mn, and Mg thathas resulted in the residual enrichment of Al and Si in thealtered rock. This pre-ore alteration is spatially associatedwith gold on a mine scale, but not on an ore-zone scale, andthe genetic relationship of this alteration to gold remainsunresolved (Penczak and Mason, 1999; Dubé et al., 2000;Parker, 2000).

Mine Geological Setting

The dominant rock type in the mine consists of variablyaltered Fe-tholeiite flows, which have previously been


Fig. 4. Simplified geology plan of the 21st level at Red Lake mine and Campbell mine, showing three major structural trends parallel toregional foliation: the Campbell Fault Trend, the Dickenson Fault Trend and the New Mine Fault Trend.

graphic marker horizon. The PK unit may represent a synvol-canic sill, or alternatively, a coarse-grained lava flow.

Minor, Balmer assemblage, sulfide-facies banded ironformation is intercalated with the mafic volcanic rocks. Thisunit is generally discontinuous and has not been used totrace stratigraphy at the mine.

Diorite and Campbell diorite (mine terminology) maybe classified as Fe-tholeiitic mafic intrusions or alternativelyas thick mafic flows. Campbell diorite may be slightly frac-tionated relative to Fe-tholeiitic basalt. Peridotite (mine ter-minology) represents Mg-tholeiitic mafic intrusions.

There are two types of rhyolite present at the Campbell-Red Lake mines. Rhyolite units in the Balmer assemblage atthe Red Lake mine are similar to rhyolite at the Campbellmine. They are generally aphanitic in texture with a waxylustre, and are transitional tholeiitic to calc-alkaline in com-position. A Balmer assemblage rhyolitic pyroclastic breccia,which hosts the H-zone sulfide ore around the 16th level ofthe Red Lake mine, contains quartz-eyes.

Lying stratigraphically above the mafic rocks of theBalmer assemblage are felsic flows, as well as pyroclastic,clastic, and chemical sedimentary rocks of the Bruce Chan-nel assemblage. Some development has cut the unconfor-mity and exposed these rocks underground. Graywacke andchert occur interbedded in variable thickness, and felsic vol-canic breccias found on the 35th level shaft station appear tograde into lapilli-tuff on surface. Rhyolite in the sedimen-tary sequence contains quartz-eyes and is calc-alkaline incomposition (Sanborn-Barrie et al., 2001). To date, no orehas been found in Bruce Channel rocks that occur within theRed Lake mine.

The volcanic and sedimentary rocks, and ore zones, atthe Red Lake mine have been intruded by post-mineraliza-tion feldspar (± quartz) porphyry (FP), metadiabase, peri-dotite, and lamprophyre dikes.

Two varieties of calc-alkaline feldspar (± quartz) por-phyry dikes have been identified. They have distinct tex-tural, and slight geochemical differences, and have differentorientations. QFP is conformable to the regional fabric,whereas, the FP is oriented east-west and dips sub-vertically.Both of these dikes may be compositionally classified asbeing the equivalent of medium-K granodiorite.

The lamprophyre dikes are massive, have chilled marginsand post-date the gold ore, the FP dikes, and most of the faultsin the environs of the mine. Two varieties of lamprophyrehave been identified. The more common melanocratic variety,which is tentatively classified as spessartite, is black, fine-grained, and calc-alkaline in composition. This variety occursas 5 ft to 10 ft (1.5 m to 3 m) wide, east-west steeply dippingdikes that are commonly oriented parallel to the regional fab-ric. A less common mesocratic variety of lamprophyre, tenta-tively classified as kerstantite, is alkaline in composition andcontains medium-grained hornblende crystals set in a gray-green fine-grained matrix. Dikes of the latter variety of lam-prophyre are typically 20 ft to 35 ft (6 m to 9 m) horizontalwidth, strike south, and dip 20° to 40° to the west.

termed “andesite.” These rocks are pillowed, amygdaloidalor massive, dark green to black, and aphanitic to fine-grained in texture. They are the main host for ore at the RedLake mine as well as the Campbell mine (e.g., see Fig. 4;21st level geology). About 85% of HGZ reserves are withinmafic volcanic rocks while the remaining 15% occur withinthe adjacent altered ultramafic rocks. The mineral assem-blage of the mafic volcanics is principally one of plagio-clase, quartz, fibrous amphiboles, biotite, minor chlorite,carbonate, hornblende, and talc. Bleached andesite (previ-ous mine terminology) is not a separate primary rock typebut represents Fe-tholeiitic basalt that has been affected bypre-ore alteration (i.e., aluminous bleaching) typified byintense cation leaching of K, Na, Ca, Fe, Mn, and Mg(Penczak and Mason, 1999).

Intercalated with the mafic volcanic rocks are highly car-bonatized and altered ultramafic rocks, of probable volcanicorigin. Two texturally and geochemically distinct varieties ofultramafic rocks are found within the mine. Altered ultramaficrock (mine terminology) is chemically equivalent to a basaltickomatiite, (BK), on a Jensen Plot, and may represent a morefractionated extrusive version of peridotitic komatiite, (PK),which was locally called “chickenfeed” or “carbonate-eye-schist.” Although spinifex textures have not been recognizedon the macroscopic scale at the Red Lake mine, other texturalevidence for an extrusive origin for the BK unit has been rec-ognized in the form of carbonate veining that defines pillowmargins (Fig. 5). Conclusive evidence for the extrusive originof the BK unit is critical in unravelling the tectonic history ofthe supracrustal rocks at the mine as it is used as a strati-


Fig. 5. Carbonate veins replacing pillow margins in BK alteredultramafic rock at entrance to fifth cut in 32-806-1 Stope. Carbon-ate vein cuts an amphibole-carbonate veinlet suggesting replace-ment at peak metamorphism.

Peridotite occurs in the footwall of the Red Lake mine,where it was intruded along the unconformity between theBalmer and Bruce Channel assemblages. Serpentine withminor biotite and carbonate alteration have been noted inthis unit on strike to the E Zone. It is not known if this intru-sion postdates the formation of the gold ore. Structurally, theunit is massive (although locally it possesses a well-devel-oped S2 fabric) and hosts minor, shallow, north-trendingcarbonate veins.

Structure at the Red Lake Mine

Different sets of fold axes that trend northwest, or northto northeast, indicate the existence of at least two directionsof principal stress during the deformation of the Red Lakebelt (O’Dea, 1999; Sanborn-Barrie et al., 2001). The overallstructure of the mine area consists of a shallow to steep, east-plunging, syncline-anticline-syncline fold repetition, definedlargely by the distribution of ultramafic marker horizons. Thedominant structure is a northwest-trending, steeply south-west-dipping, S2 foliation defined by carbonate veinlets, nar-row zones of silicification, pillow flattening, sulfide streaks,and biotite-altered areas with well-developed schistosity.This S2 foliation is axial planar to the F2 folds describedabove. An L2 lineation, defined by the elongation of varioleswithin the bleached pillowed basalt, is observed and plungesmoderately to the west (e.g., Dubé et al., 2002).

Ore structures within the HGZ occur in three trends: (1)southeast, (2) north-south, and (3) east-west and are similarto those found elsewhere in the mine (Rogers, 1992). Thesoutheast-trending structures strike about 135°, dip south-ward at 60° to 70°, and are the most common. They are sub-parallel to the regional foliation and are termed “con-formable” structures. So-called “north-south” structures,which host ore that is generally wider and has a shorterstrike length than ore associated with the other two direc-tions, typically strike 340° and dip 45° to 50° west. The“east-west” structures strike approximately 100°, dip 80°south, and have interacted with the other directions in manystopes to produce complex structural patterns (Fig. 6). Theintersection of these structures defines a lineation which issub-parallel to the L2 stretching lineation. The ore systemsare parallel to these structures and the intersection lineationdefines west-plunging ore shoots. Complex vein arrays arethose that include the north-south and east-west trends. Thecomplex arrays are most common near high-angle, mafic-ultramafic contacts (Rogers, 1992). Much of the HGZ oreoccurs in this environment, possibly due to the occurrenceof zones of enhanced dilatancy within F2 fold hinges (e.g.,Dubé et al., 2001, 2002). It is characterized by both con-formable (to regional fabric) and complex vein arrays over-printed by replacement mineralization (Fig. 7). As evidencedby stope mapping, much of the gold mineralization resultedfrom repeated episodes of brecciation and resealing of thestructure before, and during, orebody formation.


Fig. 6. Simplified geology plan of 34 level, showing folded alteredultramafic rocks, felsic volcanic rocks, shear zones and ore zones.

Fig. 7. Simplified geology plan of the HGZ, 34 level.

deformational fabrics in most of the HGZ ore sub-zones, aswell as the occurrence of boudinage in the carbonate veins.Two differing explanations for these observed features arethat post-ore regional flattening has preferentially over-printed pre-metamorphic ore in shear zones or that the orewas emplaced at peak metamorphism, and is geneticallyassociated with the shear zones. Therefore, the relative tim-ing of fabric intensity to ore formation is critical to under-standing the genesis of the HGZ, as is indicated by Dubé etal. (2001).

Ore is associated with large-scale folding of the alteredultramafic rock, considered to be an F2 antiform whichplunges southeast at 55° (O’Dea, 1999; Dubé et al., 2001).However, most HGZ sub-zones are elongated down a plungealmost due west between 45° and 55°. This is parallel to thestretching and intersection lineations and continuity of goldgrades is greatest down-plunge. On longitudinal section, thealtered ultramafic antiform rakes in the opposite direction tomost of the ore shoots (Fig. 9). However, some parts of“Main” and “Main A” sub-zones rake sub-parallel to theultramafic antiform, opposite to all the other shoots. Elon-gation lineations within these zones plunge due west, as doall the other zones. It is apparent from diamond drilling thatthere are large-magnitude changes in plunge or rolls withinthe altered ultramafic rocks. This all may be due to pre-exist-ing F1 folding perpendicular to F2, or alternatively, thiscould be caused by intersections of faults whose offsets cre-ated apparent “rolls” or changes in plunge.

A number of observations can be made about the geom-etry of the structures hosting the HGZ. The HGZ comprises15 separate sub-zones in terms of the known ore reserves.The HW5 sub-zone is the furthest in the hangingwall of theHGZ, is pipe-like in shape, and is longer and deeper than allthe other zones (Fig. 10). Its down-plunge length is over1500 ft (460 m) and it remains open below 6800 ft (2070 m)

Structure of the HGZ

It has long been recognized at both the Red Lake mineand the Campbell mine that ore zones are spatially associ-ated with known trends (such as the Dickenson and Camp-bell faults shown in Fig. 4), and that the intensity of alter-ation increases toward these trends (Rogers, 1992; Penczakand Mason, 1999). This indicates that these features arestructures that acted as feeders for mineralizing fluids risingfrom depth.

Data from the HGZ indicate a similar relationship. Inanalyzing the individual sub-zones of the HGZ, a number offeatures are observed. The Main to HW5 sub-zones, whichare the most dilatant and highest grade in the HGZ, arelocated closest to the axis of the F2 antiform that is com-posed predominantly of altered ultramafic rocks (see Fig. 7).The ore within these sub-zones consists of quartz-carbonateveins and replacement-type associated with visible gold.Those sub-zones that are in the footwall part of the HGZ,located along the north flank of the BK ultramafic unit (i.e.,FW2, FW3, and FW4), appear to be transitional in theirstyle of mineralization and gold grade, between HGZ sub-zones in their hangingwall and ESC sulfide ore in theirfootwall. That is, the FW2, FW3, and FW4 sub-zones of theHGZ are transitional from multi-ounce per ton gold quartz-carbonate vein ore of the HGZ sub-zones in the hangingwallto lower-grade 0.30 oz/t (10.3 g/t) gold, disseminated sulfidezones deeper into the footwall. Therefore, it appears that themineralizing events that affected these structures werefocussed centrally near the folded contact with the alteredBK ultramafic unit and that they were spatially associatedwith the Hanging Wall Shear (HW Shear, Fig. 8).

HGZ Structural Analysis

According to O’Dea (1999) and Dubé et al. (2001,2002), HGZ ore is spatially and genetically associated withreverse, left lateral, shear zones, and peak metamorphic,(D2), events. Underground observations indicate that thereis definitely an increase in the intensity of metamorphic


Fig. 8. Part of HW Shear in 34-876-1 South Cross-cut, 300 ft onstrike to the northwest of HW zone ore. Numerous carbonate veinsare barren. Hammer (1 ft or 0.3 m long) is located in a magnetite-silica-pyrrhotite zone, which returned 0.08 oz/t gold across 2.5 ft.

Fig. 9. Generalized vertical longitudinal section of the Campbellmine and Red Lake mine looking northeast, showing componentsof two different ore trends. The major trend is a first-order ore trendraking to the lower right at 45° and the second-order trend of indi-vidual ore zones raking oppositely to the lower left at 45°. Fourexploration targets shown here are being diamond-drilled in 2002.

depth (May 29, 2002, Goldcorp Inc. news release). Thiszone has a north-south orientation that is oblique to regionalfoliation and is a multi-stage tension gash. Its north end isbounded by the EW sub-zone and the intersection of thesetwo zones plunges sub-parallel to most of the other plunges,nearly due west at 50°. In plan view, the south end of theHW5 sub-zone thins 100 ft to 200 ft south of the EW sub-zone to a narrow area of barren carbonate veinlets. This indi-cates that the HW5 sub-zone was formed from movementalong the EW sub-zone or else that the HW5 may be a link-ing dilational jog that joins another shear in its south enddown-plunge.

The HW sub-zone of the HGZ is constrained within theHW shear and strikes sub-parallel to the regional S2 folia-tion at approximately 135°. It is located south of the axialtrace of the F2 antiform. It dips 72° south, more steeply thanthe general fabric dip of 60° south in the No. 2 Shaft area,and is 10 ft to 20 ft (3 m to 6 m) wide. The HW sub-zonehas the highest ratio of drill-hole intervals of pre-ore car-bonate veins and magnetite bands in comparison to typicalHGZ quartz vein/replacement ore type. Generally, it con-tains an erratic distribution of silicification of pre-existingcarbonate veins associated with lower gold grades in com-parison to other zones of the HGZ. A strong planar fabric,abundant carbonate stringers, boudins and veins and numer-ous strong shears and fault zones characterize the sub-zone(see Fig. 8). Asymmetry of folded carbonate veins and

boudins suggests a reverse component of motion along thesub-zone (e.g., Dubé et al., 2001, 2002). The HW sub-zonealso has the highest abundance and strength of shears andfaults in drill core of all the HGZ sub-zones suggesting thatit represents a long-lived structure. This shear contains alarge area of ore in longitudinal section, compared to theother HGZ sub-zones, and the structure that hosts the oreappears to be traceable for thousands of feet vertically aswell as horizontally, from observations made in diamonddrill core and cross-cuts. Therefore, it is a possible “feederstructure” for ore-forming fluids to the HGZ.

The best developed shear zone in the Red Lake minebelow the 30th level is called the FW shear and is located inthe footwall to the Main sub-zone of the HGZ. The FWshear is similar to the HW shear except that it contains noore reserves. It contains a strong fabric over a width of 10 ftto 20 ft (3 m to 6 m) with abundant pulled apart carbonateveins, some of which display back-rotated boudins. The spa-tial relationship of these bounding shears to the north-southzones of the HGZ indicates that movement along the shearsmay have created the dilatancy to form the north-south orestructures. The FW shear is the same structure as the “RedLake Mine Fault” (RLMF) in Fractal Graphics-Taylor WallAssociates winning submission in the “Goldcorp Chal-lenge” contest (Vic Wall, pers. comm., 2001). These authorsinterpreted the RLMF to have 2500 ft (760 m) sinistral off-set based on apparent offsets of altered ultramafic units inplan view (see Fig. 4). Fractal Graphics-Taylor Wall Associ-ates (Archibald and Taylor, 2000) interprets the RLMF tosurface from airborne magnetics surveys to represent aregional surface magnetic break that extends to theCochenour-Willans mine. This hypothesis remains to betested but the FW shear or RLMF appears to be too weakand narrow to represent the first-order regional structurecommon to most Archean gold camps (Nick Archibald, pers.comm., 2001). Such a structure seems to be missing fromthe Red Lake belt.

Minor, post-ore, “black line” faults less than an inch inwidth offset HGZ ore, up to 50 ft (15 m) both sinistrally anddextrally. These are the same thin faults found elsewhere inthe mine as well as at Campbell mine and the past-producingCochenour-Willans mine (see Rogers, 1992). Minor post-oregouge faults also less than an inch thick, commonly appearbleached or healed by silica, occur within the HGZ and jux-tapose the ore in a similar manner as the black-line faults.

Alteration

The Geology Department conducted a preliminaryalteration geochemistry program in 1999 (Penczak, 1999) tocharacterize the various alteration facies present in the mainhost rocks and to characterize alteration zonation aroundmineralized high-grade ore structures. Hydrothermal alter-ation at the Campbell-Red Lake deposit is complex, consist-ing of several superimposed, zoned, alteration events (see


Fig. 10. Vertical longitudinal section of HW5 sub-zone of the HGZ,showing contoured diamond drill results. Section is in the plane ofthe regional fabric at azimuth 135° looking northeast.

anomalous in mineralized zones since tourmaline commonlyoccurs in mineralized structures (see also Damer, 1997).

The primary composition of rock types has influencedore deposition at the Red Lake mine. High-grade Zone oreis predominantly hosted by basalt and some of the sub-zonespenetrate the BK ultramafic unit. Sulfide-type ore is hostedby basalt spatially associated with the PK ultramafic unit.Replacement type ore occurs in BK and basalt, whereas, itis generally absent in the PK unit. This variation clearlyemphasizes the importance in distinguishing ultramaficunits at the Red Lake mine on the basis of their primarycomposition.

Mineralization

The ore in the HGZ is generally characterized by rela-tively abundant distribution of both coarse and fine flecks ofnative gold, with up to 40 vol.% fine acicular arsenopyriteand 1 to 2 vol.% disseminated pyrrhotite and/or pyrite.Accessory minerals include trace amounts of fine-grainedchalcopyrite and sphalerite. Two types of sphalerite areobserved. Red sphalerite occurs in veinlets and seams and isassociated with faults and barren carbonate veins. Yellowsphalerite occurs as fine–grained disseminations in quartz-carbonate ore. Stibnite and complex assemblages of sulfosaltminerals, such as berthierite, have been noted locally in HGZore, generally near the contact with the BK ultramafic unit.

Historically, four types of ore mineralization have beenrecognized at the Red Lake mine and all are encountered inthe HGZ. These are found in complex combinations withinall three of the ore trends described above. The four typesinclude vein-type ore, disseminated sulfide ore, replacementore, and magnetite ore.

Replacement of barren carbonate veins with silica,arsenopyrite, and gold is a common texture observed in theso-called quartz-carbonate vein-type ore. Therefore, the sil-ica does not display any open-space textures and cuts thecarbonate crystals in an irregular manner.

Sulfide ore contains 2 to 7 vol.% disseminated, fine-grained, gold-bearing pyrrhotite and pyrite mineralization,sometimes found in combination with replacement type orewithin sulfide zones and HGZ of No. 2 Shaft. The host rockis generally basalt and it is always biotite altered where min-eralized with gold-bearing sulfides. This is a minor ore typein the HGZ and it usually occurs as a halo around other oretypes. There appears to be no zonation between pyrite ver-sus pyrrhotite with depth in the mine below the 30th level.

Replacement ore refers to host rocks that have been per-vasively replaced or flooded with gold-bearing silica± arsenopyrite rather than ore occurring in veins, which inreality is a sub-type of the same process. Arsenopyrite isusually fine-grained and acicular in character and present inamounts from a trace, up to 40 vol.%, of the host rock.

Magnetite ore is locally an important ore type in theHGZ, especially in the HW sub-zone and the EW sub-zone.

MacGeehan et al., 1982; Christie, 1986; Penczak andMason, 1999; Damer, 1997).

The geochemical patterns around the HGZ zones arecomplex and reflect successively superimposed alterationevents, which culminated in the mineralization stage. Alter-ation associated with mineralization is localized comparedto early alteration, which is much more widespread. Earlyalteration consists of pervasive carbonatization, togetherwith some biotitic and chloritic alteration. Also, some earlysilicification and alkali depletion appears to have been con-trolled by zones of primary permeability such as inter-pillowmargins. Mineralization-related alteration consists ofquartz-sericite, biotite, and tourmaline-bearing assemblages.It is superimposed upon early alteration and is localizedwithin portions of fault structures which were dilatant andactive during the mineralization event.

From an exploration viewpoint, the most importantalteration that is directly associated with ore mineralization isthe biotite type. Here, distinctive reddish-brown biotite(± disseminated pyrite or pyrrhotite, with anomalous goldvalues) has formed alteration halos around mineralized struc-tures: alteration haloes that are typically narrow (<1 ft to 2feet) in basaltic host rocks, but which widen considerably (upto 100 ft) where the structures cross-cut ultramafic rocks. Asa guide to exploration, the biotite alteration can be tracedalong structures for distances of 50 ft to 400 ft along strikebeyond the limits of ore grade mineralization (Fig. 11).

From the Geology Department’s preliminary program,alteration associated with mineralization is typified by theaddition of Si, K, S, CO2, As, Sb, Tl, Te, Se, and Rb and bythe loss of P. Potassium seems to be especially enriched inmineralized zones compared to other K-mica-bearing alter-ation zones (i.e., biotite-carbonate). Boron is likely to be


Fig. 11. Folded carbonate veins in 34-876-1 South Cross-cut, 400ft on strike to the northwest of Main B sub-zone HGZ ore reserves.Folded carbonate vein on right has a biotite selvedge. Thinnerfolded carbonate vein on left is infilled with amphiboles in inter-boudin necks. This shows deformation of veins during F2 shorten-ing first by folding then by reverse faulting as seen on vein offsetin lower right part of photo. Hammer in center is 1 ft (0.3 m) long.

It is characterized by massive fine-grained magnetite, whichis variably brecciated and infilled with minor quartz orreplacement ore or visible gold in fractures. Magnetite ore isfound in basalt as well as the BK ultramafic unit.

Gold Grade Estimation

Grade estimation of the extremely rich ore of the HGZpresented a unique challenge for the Geology Department(visible gold is a mappable unit). Prior to mining, over 85%of HGZ intercepts from definition diamond drilling dis-played visible gold, which was unprecedented. The mainissues were how much cutting of high-grade assays wouldbe appropriate to estimate the true metal content of the HGZore and how continuous was the complexly shaped orebetween drill holes. Accuracy of grade estimation starts withthe collection of high-quality data, and clearly only the pro-duction data could in fact verify that the correct cutting pro-cedure was used.

Analysis of Grade Estimation for the HGZ

Data Control and Collection

Production geologists and samplers at the mine provideunderground coverage on both day shift and night shift, 365days a year. Large amounts of data are collected from chipsamples, muck samples, and test holes for virtually everyblast in ore. For example, approximately 37 000 assay deter-minations were made for chips, mucks, and test holes duringthe year 2000 development of the HGZ.

The chip sample, test hole, and muck sample data areentered twice daily, into the “ORE2B” database, which isused as a monitoring center for ongoing grade and dilutioncontrol progress as well as dilution assessment and the cre-ation of ore outline grades. The database is summarized inan elaborate set of pivot tables that attribute various cut goldgrades, tonnage, location, geology, and internal and externaldilution to every single blast of ore in the mine. It is alsoused to alert production geologists to excessive dilution thatmay have occurred on the previous shift so that it can beimmediately addressed. Linking the mapping with assayplans is also used to analyze trends.

Chip Sampling

During the silling program on the 34th level and 32ndlevel in year 2000, two rows of chip samples were collectedfrom the face or walls of each blast in ore (Fig. 12). Gener-ally, the rows were three to four feet apart in elevation. Aweighted average for grade was determined for each blastbased on the assay results of those samples influencing thegrade of the volume blasted. Once mining above the sills

began, sampling reverted to one row for each blast. Thesesamples are collected at the mid-lift elevation. The produc-tion geologist plots the location of each chip string at theface underground by tying it into a surveyed location usinga pocket laser protractor and a pocket laser distance meter.

Muck Sampling

Muck (blasted rock) samples have been collected fromvirtually all of the ore blasts during the silling and subsequentmining. In addition, muck samples are collected daily fromcars tramming between No. 2 and No. 1 shaft on the 23rdlevel, and on surface as material goes to stockpile. Generally,four to eight muck samples are collected per blast (average100-ton blasts), with sample numbers varying with tonsblasted. One sample was collected for every three carstrammed on the 23rd level, for an average of 1 sample per 12tons (10.9 t). On surface, one muck sample was collected forevery 9 tons (8.2 t) brought to stockpile. Uncut muck samplesprovided a reasonable estimate of the ore grade on a per levelbasis and on a global basis but not always on a stope basis.Thus, given an adequate sample population, uncut muck sam-ples accurately reflect the overall grade of the broken ore.

Drill Core Sampling and Assaying

In drill core, all identified mineralized structures arewhole core-sampled or else half-core sampled using a dia-mond saw. The remaining half core is saved for future refer-ence, some for metallurgical testing. Sample lengths are typ-ically two to three feet or shorter in the higher-gradesections. Since 1998, an effort has been made to standardizesample lengths at 2 ft (0.6 m) intervals in mineralized zones.


Fig. 12. Production geologist Nick Cianci at a mining face on aquartz-carbonate vein in the HGZ. Two vertical paint lines acrossface represent chip sample intervals.

mated 35% increase in ounces mined up to December 31,2000 versus the 1999 ore reserve estimate using the histori-

All samples from the HGZ have been assayed for goldusing primarily 1 assay-ton fire assay with a gravimetric fin-ish. Metallic screen assay methods have been used for sam-ples with visible gold or for samples where fire assay resultsreported more than 20 oz/t (685.7 g/t). Routine assay checkswith standards are conducted, two standards and threeblanks inserted per 100 samples collected.

Basic Statistics

Log Normal Probability plots were derived from over7700 assays from 1542 drill hole intersections inside theresource outlines of the HGZ. Before cutting the high val-ues, the data were normalized to equal lengths of two feet,as the high-grade assays tend to be shorter and the low-gradesamples longer than average. Plots of normalized uncutsamples for the entire HGZ, as well as individual sub-zones,are linear. No discontinuity is present to indicate the level ofcutting that should be used (Fig. 13). This indicates that theHGZ has one population. Plots using non-normalized sam-ple lengths as well as chip sample data display similarresults. Typically, such as in lower-grade sulfide ore at themine, two populations of gold are recognized in the log nor-mal curve, which is used to select the top cutting figurebased on a change in slope in the upper range.

The two gold populations found in sulfide ore may rep-resent gold emplaced with disseminated sulfides in the wall-rocks and gold in quartz veinlets. It is difficult to envision asingle geological event for the emplacement of the HGZ oreand its single gold population. Underground observations ofmutually cross-cutting ore textures, as well as late remobi-lization of gold in fractures, indicates a process that wasrepeated a number of times, which had added as well as“homogenized” the gold by redistributing it throughout theHGZ each time.

Cutting Factor

The historical cutting procedure was initially adopted tocalculate gold grade in the HGZ when it was outlined bydiamond drilling (see Fig. 14). The cutting procedure hasbeen refined twice since then as more data were collectedfrom mining and mill reconciliation.

Prior to year 2000, the historical “2-5-10” cutting wasused for the HGZ to reduce individual high grades, whichwere considered to have low probability for geological con-tinuity. The 2-5-10 cutting factor means that all individualassays below 2 oz/t (68.6 g/t) are left uncut, assays between2 oz/t (68.6 g/t) and 5 oz/t (171.4 g/t) are cut to 2, assaysbetween 5 oz/t (171.4 g/t) and 10 oz/t (342.9 g/t) are cut to10, and all individual assays above 10 oz/t are cut to 10. Arevised cutting factor was used for the 2000 resource calcu-lation on the HGZ due to reconciliation with production data.The one standard deviation cut closely approximated the esti-


Fig. 13. Distribution of gold assays from the HGZ: a) log normalhistogram; b) log normal probability plot.

Fig. 14. A 3D long section view of the Red Lake mine lookingnortheast, showing mine workings, reserves (some previouslymined) and resources. Red dots represent drill hole intercepts grad-ing more than 1 oz/t gold. Key trend is an east-west corridor.

cal cutting procedure. This means that individual assays werecut using a mean plus one standard deviation cutting factorthat reduces assays greater than 15 oz/t (514.3 g/t) to 15.

It became apparent from reconciliation with mining datain 2001 that a cutting procedure of mean plus one standarddeviation was still underestimating grades. The GeologyDepartment analyzed the ore outlines and sample data with the“ORE2B” spreadsheet in monthly grade reconciliation withstope surveyed data and mill bullion data. This reconciliationprocess correlated with a cutting procedure of mean plus threestandard deviations or a cutting factor of 39 oz/t (1337 g/t)gold for the HGZ. Therefore, the 3SD cut has been adopted forore reserves. The largest increases of reconciled grades fromthe refinement of the cutting factor came from Main, HW5,and EW sub-zone ore. There was very little effect in the FW2,FW3, and FW4 sub-zones from this change. A glance at a typ-ical chip assay plan from a Main Zone stope illustrates theabundant distribution of high gold grades (Fig. 15).

HGZ ore reserves calculated in July 2001 increased to1.9 million tons (1.73 Mt) at a grade of 2.02 oz/t (69.3 g/t), fora total gold content of 3.02 million ounces. Refinement of thecutting factor resulted in the ore reserve grade increasing by20% from year-end 2000 (September 12, 2001 news release).

Discussion

It is beyond the scope of this paper to address the tim-ing and genesis of ore formation as well as geological rea-soning for the exceptionally high grades. These are contro-versial and are currently being investigated by Dubé et al.(2001, 2002). However, some observations can be madehere, recognizing the inherent risk that there is the possibil-ity of too narrow a focus in the present study.

For example, prior to the discovery of the HGZ, it wasgenerally thought that only lower-grade, disseminated-sul-fide-type ore would be found in the amphibolite facies meta-morphic rocks, as mining progressed toward the deeper, east-ern part of the Red Lake mine. The early mining took place inthe upper west part of the mine where ore came from high-grade, carbonate-quartz veins within greenschist facies vol-canic rocks characterized by chlorite-Fe-carbonate alteration(Damer, 1997). As mining progressed, this gradually gaveway to lower grade ore dominated by disseminated sulfides,where the volcanic wallrock alteration is largely actinolite andbiotite. The discovery of the HGZ in the deep eastern portionof the mine has thus challenged the conventional dogma ofthat time, which inferred high-grade vein ore could not occurin amphibolite facies rocks because brittle fractures would notbe open to gold emplacement in such a setting. Regardless ofhow the HGZ was deposited, it appears that the structuresintersecting a folded contact of BK ultramafic unit were a keyfactor in localizing the ore and that the recognition of similarenvironments elsewhere is critical in discovering more high-grade orebodies. Therefore, the greenschist/amphibolite iso-grad can be ignored for exploration purposes.

Ore textures in carbonate veins and cross-cutting rela-tionships indicate peak-metamorphic or D2 emplacementfor at least some of the gold (see also O’Dea, 1999; Dubé etal., 2001, 2002). Basalts adjacent to HGZ ore host barrencarbonate veins, which exhibit open-space textures and con-tain no gold. The narrower carbonate veins adjacent to, andwithin ore, commonly exhibit boudinage as the ore zonesare spatially associated with shear zones. The inter-boudinareas are usually infilled with amphiboles suggestingdeformation at peak-metamorphic conditions (Fig. 16).High-grade Zone ore composed of silica, fine-grainedarsenopyrite, and native gold that replaces carbonate veinshas been observed cutting interboudin amphiboles as well assome of the amphiboles being emplaced along the silica-car-bonate boundary (Fig. 17). This has been observed in twostopes on the 34th level, one stope on the 32nd level, andone on the 36th level. This indicates that this period of oreemplacement occurred at peak metamorphism. It ispresently poorly understood how much earlier the ore-bear-ing structures were open to gold mineralization.

Barren carbonate veins exhibiting open-space tex-tures have been observed as occurring in both pre- andpost-ore settings, which is consistent with observationselsewhere in the mine (Rogers, 1992). For example, ESCore is cut by barren carbonate veining in one location in16-017 Stope. High-grade Zone ore usually replaces bar-ren carbonate veins, but has also been observed to containpost-ore barren late carbonate veining, which suggeststhat a complex multi-stage mineralizing process over-lapped with a barren event many times (Fig. 18). Recentdrill results on the 37th level suggest that abundant barrencarbonate veining is spatially associated with ore ratherthan the contact with the ultramafic antiform there. There-fore, with depth, both the carbonate veining and the ore


Fig. 15. A 3D view of a typical chip plan of HGZ ore from theMain Zone, fourth cut in 34-786-2 Stope. Individual chip samplesare taken across the face and walls as two-foot lengths. Numbersare uncut ounces per ton gold (not grams!).

and Main sub-zone ore in 32-826-1 Stope (see Fig. 1). Thetiming of the flat fracture gold remobilization is unknown butmay be the same as that of the post-lamprophyre event.

Mine Scale Dilatant Corridors

The first-order trend (or the “horizon trend” of Rogers,1992) of the gold generally follows contacts with ultramafic

move down-plunge away from the ultramafic antiform.This also indicates a genetic relationship between barrencarbonate veining and ore and structure.

Post-lamprophyre dike remobilization of gold has beenobserved in the HGZ. A lamprophyre dike exhibiting chilledmargins, striking 100° and dipping 80° north, intruded Mainsub-zone ore in 32-826-1 Stope and contains native goldplating a fracture cutting across ore and the dike (Fig. 19).Another lamprophyre dike with chilled margins, striking at010° and dipping 25° east across HWA sub-zone ore in 37-846-2 Stope, was also found to contain gold plating a frac-ture cutting across ore and the dike. Late gold remobilizationplating sub-horizontal fractures has been observed in the“Jewelry Box” area of HW sub-zone ore in 34-806-2 Stope


Fig. 17. Ore sample from the HW5 zone of the HGZ, sill cut in 36-746-1 Stope. This shows silica containing fine arsenopyrite andnative gold cutting an iron-carbonate vein with inter-boudinamphibole bands, indicating that this mineralizing event occurredat peak metamorphism. Scale is in inches.

Fig. 16. Boudinaged carbonate vein, from HW zone of the HGZ,first cut in 34-806-2 Stope. Inter-boudin bands are composed ofamphiboles which is consistent with formation at peak-metamor-phic conditions. Pen at bottom for scale is 1 cm wide.

Fig. 19. Lamprophyre dike (upper left) cutting HGZ Main sub-zone ore in first cut, 32-826-1 Stope. Fracture containing nativegold (bright patches) extends into the lamprophyre dike demon-strates that gold has been remobilized during post-dike time.

Fig. 18. Ore specimen from HGZ Main Zone ore in sill cut, 34-786-1 Stope. Carbonate vein exhibiting open space textures, cutsbrecciated quartz containing visible gold that was recemented witharsenopyrite-silica. Pen at top for scale is 1 cm wide.

units and rakes in a nearly opposite direction in longitudi-nal view as individual ore zones (see Fig. 9). From analyz-ing the first-order ore trend and constructing a 3-D enve-lope, a southerly dilatant corridor is identified that trends170° and plunges 48°. This corridor is oblique to theregional fabric and is characterized by the en-echelon stopearrays that step to the south, as one observes their arrange-ment from surface to depth going southeast toward theHGZ. This indicates that with further depth to the south, theHW7 shear in the hangingwall to the HGZ may have highpotential to host ore.

Similarly, an East-West vertical dilatant corridor isindicated by the east boundary of almost all the HGZ orereserves, which is typified by the HW5 sub-zone. This cor-ridor is centered about engineering grid line, 0N (Fig. 20)oblique to regional foliation. New ESC mineralization fromdrill intercepts east of stopes around the 15th level lines upwith this East-West dilatant corridor as well. This corridorhas the same strike and dip as the EW sub-zone, as well aspost-ore FP dikes and some lamprophyre dikes nearby tothe HGZ. This suggests that the geological processesresponsible for these features were either a long-lived eventor a re-activation event. This corridor does not correlatevery well with contacts of ultramafic units and the processresponsible for its creation is poorly understood.

An exploration target within the East-West corridor isapparent where the down-plunge line of the HW5 sub-zoneore intersects with HW7 shear. HW5 is a north-south trend-ing multi-stage tension gash oblique to regional fabric,which is consistent with its propagation as a dilational jogbetween two bounding shears. HW7 shear on 34 levelappears to have been too far away into the hangingwall fromthe intersection of HW5 and EW zones, so that in plan viewthe HW5 ore does not extend southward all the way to HW7.However, at depth the HW7 shear is possibly a “dilatant tar-get” of intersection with the oblique HW5 Zone (see Fig.20). Recent deep drill results have encountered four sub-zones of HGZ mineralization up to 3.53 oz/t gold over58.0 ft, at a depth of 6850 ft below surface. One of the fourzones intersected was the HW5 sub-zone which returned4.40 oz/t gold over 4.4 ft and remains open at depth (May29, 2002, Goldcorp news release).

Exploration

Historically in gold exploration, empirical models havebeen more successful than genetic models in finding ore-bodies (Thompson, 1993). The wide range of proposedgenetic models reveals our poor understanding of the com-plex processes involved in the formation of gold deposits.The Red Lake camp is no exception as genetic models pro-posed for ore at the Campbell-Red Lake deposit range fromepithermal to syn-metamorphic processes. Furthering ourunderstanding of the genesis of the HGZ is critical in dis-covering more ore in a cost-effective and timely way. This isthe reason for selected teams of experts who are collecting,measuring, and interpreting data as the HGZ is being openedup. However, as time is of the essence, the Red Lake minegeology team is using empirical observations to drive explo-ration as they strive to unravel the genetic complexities ofthe deposit. The risks in modelling are two-fold: a possibleover-emphasis on local features that are not important at alarger scale or conversely a reliance on the attributes of asingle process that may reduce a complex genesis to a sim-ple panacea (Thompson, 1993).

It is the recognition of key geological relationships atthe Red Lake mine that is the basis for mine exploration.Three main structural zones or fault trends are known at theCampbell-Red Lake deposit, each consisting of anastomos-ing and/or intersecting subsidiary structures, which from thefootwall in the northeast to the hangingwall in the south-west, as shown in Figure 4, are:

1. The Campbell Fault Trend hosts or is spatially asso-ciated with the G, B, (parts of) L, and NL zones at Camp-bell, and the F, D, and ESC4 zones at the Red Lake mine.

2. The Dickenson Fault Trend hosts or is spatially asso-ciated with the F, A, P, and AU zones at the Campbell mine,and the SC and ESC zones at the Red Lake mine.

3. The most poorly defined structural trend occurs in thehangingwall and appears to be associated with the S Zone as


Fig. 20. Simplified geology in east-west cross-section on engineer-ing section 0N, from surface to the hypothetical 41st level. This isparallel to the plunge of HGZ ore and oblique to the regional fab-ric. Ore (in red) is localized beneath folded altered ultramafic at theintersections of shear zones. Exploration targets shown are cur-rently being diamond-drilled.

Penna, Jim Bryce, Nick Cianci and Dayle Rusk. Other pro-duction geologists are also thanked for their input: MarkEpp, John Kovala and Mike Collins. The surface explorationgeologists Kim DaPrado and Jenn MacLachlan, and corpo-rate geologist Michael Dehn, are thanked. Gilles Filion, vice-president of exploration, Goldcorp Inc., is also thanked.Arlene Connolly is thanked for her drafting.

Constructive review by Benoît Dubé and KenWilliamson has helped to improve the manuscript. They arealso thanked for their excellent professional interaction aswell as numerous constructive discussions underground “atthe mining face.” As iron sharpens iron, so we sharpen oneanother.

References

ANDREWS, A.J., HUGON, H., DUROCHER, M., CORFU, F.and LAVIGNE, M.J. 1986. The anatomy of a gold-bearinggreenstone belt: Red Lake, northwestern Ontario, Canada.In Proceedings, Gold’86, an international symposium onthe geology of gold deposits. Edited by A.J. Macdonald.Konsult International Inc., Toronto, p. 3-22.

ARCHIBALD, N. and TAYLOR, V. 2000. Goldcorp, Red LakeRiches. Re-submission for Goldcorp’s Challenge contestby Fractal Graphics-Taylor Wall Associates. Goldcorp Inc.Internal Report.

CHRISTIE, B.J. 1986. Alteration and Gold MineralizationAssociated with a Sheeted Veinlet Zone at the CampbellRed Lake Mine, Balmertown, Ontario. M.Sc. thesis,Queen’s University, Kingston, 334 p.

DAMER, G.C., 1997. Metamorphism of Hydrothermal Alter-ation at the Red Lake Mine, Balmertown, Ontario. M.Sc.thesis, Queen’s University, Kingston, 195 p.

DUBÉ, B., BALMER, W., SANBORN-BARRIE, M., SKUL-SKI, T. and PARKER, J., 2000. A preliminary report onamphibolite-facies, disseminated-replacement-style min-eralization at the Madsen gold mine, Red Lake, Ontario.Geological Survey of Canada, Current Research 2000-C17, 12 p.

DUBÉ, B., WILLIAMSON, K. and MALO, M., 2001. Prelim-inary report on the geology and controlling parameters ofthe Goldcorp Inc. High-grade Zone, Red Lake mine,Ontario. Geological Survey of Canada, Current Research2001-C18, 13 p.

DUBÉ, B., WILLIAMSON, K. and MALO, M., 2002. Geologyof the Goldcorp High-grade Zone, Red Lake mine,Ontario: An update. Geological Survey of Canada, CurrentResearch 2002-C26, 13 p.

DUROCHER, M.E., 1983. The nature of hydrothermal alter-ation associated with the Madsen and Starratt-Olsen golddeposits, Red Lake area. In The Geology of Gold inOntario. Edited by A.C. Colvine. Ontario Geological Sur-vey, Miscellaneous Paper No. 110, p. 123-140.

MacGEEHAN, P.J., SANDERS, T. and HODGSON, C.J.,1982. Meter-wide veins and a kilometre-wide anomaly:Wall-rock alteration at the Campbell Red Lake and Dick-enson gold mines, Red Lake district, Ontario. CIM Bul-letin, 841, p. 90-102.

well as the newly discovered DC Zone at the Campbell mineand the HGZ, and PLM zones at the Red Lake mine. Thisstructural trend is tentatively called the New Mine Fault Trend.

The term “fault” means zone of structural anisotropyand does not imply either a brittle or ductile regime. Thethree structural zones are also associated with large deflec-tions and offsets of folded lithological units throughout thedeposit. Therefore, competency contrasts between differentlithological units within these trends have played a veryimportant role in localizing ore as has been pointed out inthe past. It is important to note that all three structural trendscontain, or are spatially associated with, high-grade stylemineralization and/or sulfide mineralization. Along theirstrike length, all three may either be mineralized or containslivers of faulted, highly altered, but unmineralized, wall-rocks several hundreds of feet long.

Dilatancies along major structural zones were the keyelements for localizing ore at the Red Lake mine. The explo-ration strategy is to identify and delineate fault structuressub-parallel to the regional foliation and systematicallydefine them. These are the first-order targets and easiest toidentify because of their large extent. This often results in tar-gets of projected intersections of faults. Other targets includefolded BK ultramafic rock contacts that are along strike withfault structures. Large sulfide orebodies are targeted wherefault zones intersect PK ultramafic rock units. Lithologicalcontacts that display offsets or deflections are also targeted.On-strike projections of the major fault trends eastward intothe high-angle folded contact with the Bruce Channel assem-blage (re-interpreted as the new Huston assemblage by San-born-Barrie et al., 2001) are also exploration targets.

It is important to note that exploration of one target typeis not exclusive of any of the other types of targets — theycan be found near to each other as is clearly demonstratedby the history of discovery at the Red Lake mine. A high-priority exploration target at the Red Lake mine is to findanother HGZ or another Campbell mine L Zone, which arein a similar geological setting. In both the L Zone and theHGZ, ore formed where a fault trend in basalt intersectedfolded BK ultramafic rock that created a semi-permeablecaprock to ore fluids ascending the “feeder” structure (seeFig. 20). This was enhanced by strong competency contrastsamong the ultramafics, felsic volcanics west of the ore, andthe mafic volcanic host (see Fig. 6) — an exceptional envi-ronment to develop protracted dilatant fluid pathways forgold deposition.

Acknowledgments

Every geologist at the Red Lake mine contributed to thispaper in one way or another. The exploration team of RobPenczak, Mark Croteau and Matt Ball are thanked for theirinsightful input and review. Mine production geologists arethanked for their meticulous attention to geologic detail: PaulBarc, Ron Sinkiewicz, Steve Duenk, Rick Sproule, Dave


O’DEA, M., 1999. Goldcorp Inc. unpublished internal report, posted on www.goldcorp.com in \challenge\references\structure.

PARKER, J.R., 2000. Gold mineralization and wall-rock alter-ation in the Red Lake greenstone belt: A regional perspec-tive. In Summary of Field Work and Other Activities.Ontario Geological Survey, Open File Report 6032, p. 22-28.

PENCZAK, R. 1999. Geochemistry of alteration around somehigh-grade zones and geochemical characteristics ofaltered rocks at the Red Lake mine. Internal report postedon www.goldcorpchallenge.com/challenge1/usefulinfo/geochem_alteration.pdf.

PENCZAK, R. and MASON, R., 1997. MetamorphosedArchean epithermal Au-As-Sb-Zn-(Hg) vein mineraliza-tion at the Campbell Mine, northwestern Ontario. Eco-nomic Geology, 92, p. 696-719.

PENCZAK, R.S. and MASON, R., 1999. Characteristics andorigin of Archean premetamorphic hydrothermal alterationat the Campbell Mine, northwestern Ontario, Canada. Eco-nomic Geology, 94, p. 507-528.

ROGERS, J.A., 1992. The Arthur W. White mine, Red Lakearea, Ontario: Detailed structural interpretation the key tosuccessful grade control and exploration. CIM Bulletin,957, p. 37-44.

SANBORN-BARRIE, M., SKULSKI, T., PARKER, J. andDUBÉ, B., 2000. Integrated regional analysis of the RedLake belt and its mineral deposits, western SuperiorProvince, Ontario. Geological Survey of Canada, CurrentResearch 2000C-18, 19 p.

SANBORN-BARRIE, M., SKULSKI, T. and PARKER, J.,2001. Three hundred million years of tectonic historyrecorded by the Red Lake greenstone belt, Ontario. Geo-logical Survey of Canada, Current Research 2001-C19,19 p.

STOTT, G.M. and CORFU, F., 1991. Uchi Subprovince. InGeology of Ontario. Ontario Geological Survey SpecialVolume 4, Part 1, p. 145-236.

THOMPSON, J.F.H., 1993. Application of deposit models toexploration. In Mineral Deposit Modeling. Edited by R.V.Kirkham, W.D. Sinclair, R.I. Thorpe and J.M. Duke. Geo-logical Association of Canada, Special Paper 40, p. 51-67.

ZHANG, G., HATTORI, K. and CRUDEN, A.R., 1997. Struc-tural evolution of auriferous deformation zones at theCampbell mine, Red Lake greenstone belt, SuperiorProvince of Canada. Precambrian Research, 84, p. 83-103.


geology and estimation of high grade zone at red lake mine

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