preliminary report on detrital gold assessment …

PRELIMINARY REPORT ON DETRITAL GOLD ASSESSMENT

DIAMOND DRILLING SURVEY NASIVI DELTA, TAVUA, FIJI

13 November – 4 December 2000

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[SOPAC Technical Report 319 – Wong & Lum]

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TABLE OF CONTENTS

Page

SUMMARY.................................................................................................................... 5 ACKNOWLEDGEMENTS ............................................................................................. 4 OBJECTIVES................................................................................................................ 6 INTRODUCTION .......................................................................................................... 7 CLIMATE ...................................................................................................................... 7 VEGETATION............................................................................................................... 7 PHYSICAL SETTING.................................................................................................... 9 ACCESS ....................................................................................................................... 9 GEOLOGY.................................................................................................................. 10 PERSONNEL INVOLVED........................................................................................... 10 GEOGRAPHIC LOCATIONS...................................................................................... 11 DRILLING PROCEDURE – SAMPLING TECHNIQUE ............................................... 11 RESULTS ................................................................................................................... 14 CONCLUSIONS.......................................................................................................... 14 RECOMMENDATIONS............................................................................................... 14 REFERENCES ........................................................................................................... 15

LISTS OF FIGURES Figure 1. Locality map and caldera geology................................................................. 8 Figure 2. Location of drill holes positions ................................................................... 12

LISTS OF PLATES MRD’s Tone Top 250 drilling rig.......................................................................Title page Plate 1. Part of survey area covered by sugar cane fields ........................................... 9 Plate 2. Part of road leading to survey area covered with flood water ....................... 10 Plate 3. Drill rig in operation ....................................................................................... 13

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ACKNOWLEDGEMENTS The Government of the Republic of Fiji funded the survey with additional funding from the Government of Taiwan. Mineral Resources Department (MRD) and South Pacific Geoscience Applied Centre (SOPAC) provided the logistic support and assistance for the survey. Thanks are due to the Tui Tavua and landowners of the Nasivi Delta area for granting us permission to work in the area. We would also like to acknowledge the contribution made by Livai Bulisolevu, Waseroma O’Connor and the drilling staff, Samuela Magititabua, Isireli Tikomaitoga and Waisale Ravarava, namely for their hard work in the field.

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SUMMARY

MRD and SOPAC jointly undertook a drilling program in the Nasivi Delta area, Tavua, from 14th November to 02nd December 2000 for detrital gold. This drilling programme was a follow up from a drilling programme undertaken in 1999. Five holes were drilled using a diamond drill. Depths ranged from 27 to 42.4 m. Core samples were collected inside a split tube liner inside the barrel. Materials encountered were consolidated sand, weathered basalt, stiff clay, and gravel. Last year no core was recovered as the drilling method used only allowed sludge to be collected. Recovery was poor when sand was encountered so the sludge was also collected. For clay, recovery was nearly always 100%, unless the barrel was jammed. Panned concentrates of samples collected from drill hole TV99/4 showed that gold flakes existed in the area. Therefore, our first drill hole, TV00/1, was located on the same site. This hole was terminated at 40.5 m when stiff plastic clay was encountered. The locations of the drill holes were spread over the area covered by the geophysical survey conducted in 1998 so as to cover a wide range, even though some of the drill holes were sited on non-targeted areas. Panning on-site of sludge (TV00/4) revealed gold flakes in one of the drill holes. This is to be confirmed by further work on the samples collected. Samples collected are to be split in half, one for storage, and the other for processing which will include panning and chemical analyses. Results of this work will determine whether further work is to be carried out in Tavua in the future, but the samples collected are encouraging as detrital gold is present.

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OBJECTIVES

The primary objective of the Detrital Gold Resources Survey in the Nasivi Delta Area was to assess the placer gold potential in the sediments of the Nasivi Delta, particularly the gravel beds, by drilling, using the MRD-owned GEMCO drilling rig. To meet this objective a drilling programme consisting of five drill holes was conducted. Field programme aims included: • conducting a drilling programme in target areas identified from the EM and resistivity

survey conducted in the Nasivi River delta, • assessing the placer gold potential of the samples collected by panning, and

microscopic examination of the heavy-mineral concentrate, and • chemical analysis of core samples collected. This work was carried out to fulfil the requirements of Task FJ97/02, and the field programme was conducted from 13 November and 04 December 2000.

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INTRODUCTION

This drilling survey was undertaken to assess the potential for detrital gold in the area within and adjacent to the Nasivi River delta on the north coast of Viti Levu, in the vicinity of Emperor Gold Mines in Vatukoula (Figure 1). This initiative is a result of a recommendation of a review of placer gold potential of Nasivi Delta area following geophysical work conducted earlier. The Nasivi Delta area was chosen because it is geologically favourable and it is near a known mining goldfield, the Tavua Goldfield. As the Nasivi River cut through the mineralised rocks, both detrital gold and gold-bearing rock fragments have have been washed down the river to accumulate in the delta and adjacent offshore areas. This diamond drilling programme is a continuation of work carried out in 1999 with rotary drilling of eight drill holes. Gold grain was observed in two of those drill holes. This is a preliminary report which only discusses the results of the panning carried out on the sludge samples collected. A detailed report will be written when the samples are submitted for chemical analysis and the results received.

CLIMATE The survey area lies on the north coast of Viti Levu and like the rest of Fiji enjoys six months each of “summer” (hot and wet) and “winter” (cool and dry). Average rainfall for the area is 1860 mm per annum that falls generally throughout the wet season (November to April), which also happens to be the cyclone season. The Nasivi Delta area is also prone to flooding and flood levels may reach at least 2 m.

VEGETATION Much of the study area is covered by sugar cane fields. Sugar cane is normally harvested during June to December. Therefore the later part of this period provides the best working period in the area because of the absence of sugar cane.

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Figure 1. Locality map and caldera geology

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Plate 1. Part of the survey area covered by sugar cane fields

PHYSICAL SETTING The Nasivi River delta lies approximately at 177

o40' E and 17

o33' S (see Figure 1) on the

northern coast of Viti Levu, close to Tavua. The alluvial sediments of the dominantly subaerial delta are derived from the Nasivi River that drains the Tavua Caldera, which hosts the Vatukoula gold deposit approximately 10 km upstream from the present mouth of the Nasivi River, which flows into the internal embayment, the Taba-Ko-Nalomo Passage at the western extent of the survey area. The approximate dimensions of the Nasivi River delta are 5 km east-west, and 3 km north-south. Water depths in the main channel vary between 5 and14 m. The delta area is surrounded by extensive and well-developed coral reefs, Sali Sali and Ve Drala reefs to the north, and Olaca Reef to the east. Olaca Reef separates Taba-Ko-Nalomo Passage from Natobu-Drauivi Passage, in Tavua Bay. These three reefs are exposed at low tide and are separated by deeper water with average depth15 m. The Nasivi Delta flood plains is generally low lying along the coast grading into undulating countryside. The terrain in the interior is hilly and deeply dissected. Rock exposure is poor and weathering is intense. Most of the land is cultivated by sugar cane.

ACCESS The area is reached from the tar sealed Kings Road and also from Tavualevu Village end over an Irish crossing except in flooded conditions. It is serviced by numerous all-weather cane roads. During heavy rain the cane roads are often flooded in places, but it is accessible to traffic. There are also numerous boat landing sites along the coast.

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Plate 2. Part of road leading to survey area covered with flood water.

GEOLOGY Blatchford (1953), Cohen (1962), Ibbotson (1967) and Setterfield et al. (1991) discussed the geology of the Tavua area in detail (Figure 2). The Emperor Mine is located on the western rim of the Tavua caldera. The caldera formed at the centre of a shoshonitic volcano, which developed in a submarine to later subaerial environment. Avalanche deposits overlain by lacustrine sediments, shoshonite lavas and hydrovolcanic/pyroclastic lapilli tuffs are found within the caldera. Dominant rock types on the flanks of the caldera are lava flows which are mainly absarokite in composition, together with debris flows and conglomerates (Setterfield et al 1991).

Gold mineralisation is epithermal and is largely structurally controlled. Gold occurs in quartz-telluride veins within three structural environments (flatmakes, steep shears and shatter zones). Mineralisation varies in width from millimetres to tens of centimetres. Quartz and carbonate are the major gangue minerals. The ore minerals are gold-silver tellurides, native tellurium, native gold, and gold-bearing pyrite, with rare occurrences of native silver.

PERSONNEL INVOLVED The drilling project for assessing the potential of detrital gold in the Nasivi Delta area sediment was undertaken by personnel from MRD and SOPAC.

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MRD SOPAC H.L. Wong Marine Geologist Jackson Lum Marine Geologist Isei Rayawa Technical Officer

II Sekove Motuiwaca

Geological Technician

Livai Bulisolevu Drilling Superintendent

Waseroma O’Connor

Techical Officer II

Samuela Magititabua

Drill Crew

Waisale Ravarava

Drill Crew

Isireli Tikomaitoga

Drill Crew

GEOGRAPHIC LOCATIONS

Drill hole locations were fixed with a handheld GeoExplorer GPS. Gamin Rover GPS with Differential Del Notre with reference to the 4600 GPS receiver which was set up at the Tavua Reservoir (WGS 84 reference point LAT 17o 25’ 55.7453”S, LONG 177o 51’ 46.0094”E, Height 115.8980 m).

DRILLING PROCEDURE – SAMPLING TECHNIQUE The MRD-owned GEMCO N22A truck-mounted drill rig was used to drill five vertical holes in the targeted area (Figure 2). NMLC Barrel with split inner tube was used to collect the core samples. The barrel size is 3.5 m x 72.2 mm (Outer diameter) x 55 mm (inner diameter). “NW” size drilling rod was used to drill the hole. The rod size is 3050 mm x 65 mm (outer diameter). As drilling progressed the hole was cased every six metres using “NX” size casing. Casing continued where possible. The specifications of the casings are 3 m x 90 mm(outer diameter) x 75 mm (inner diameter). A tungsten carbide roller-face drill bit was used to drill the holes.

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The drilling method used was coring with a diamond-impregnated bit, with water/drilling-mud circulation. A sump, approximately one cubic metre, was near the drill site and was filled with water, which was used for drilling purposes. As drilling proceeds the samples (cores) are collected in an NMLC Barrel with split inner tube, and as water plus mud is pumped down it brings the sludge up. For each metre drilled, the water plus sludge is collected in buckets and the water is then poured out. The samples are collected in labeled bags and logged on site. The logging is confirmed on return to the office, when the samples are panned and microscopically examined. The drill cores collected will be processed and submitted for chemical analysis. This diamond drilling is not the best method, as sample recovery at times was very poor, especially if sand was encountered. This is because sand could not be collected in the split tube, hence the collection of the sludge.

Plate 3. Drill rig used in 1999 in operation. In the foreground is the sump filled with water The methodology of sample collection and the use of drilling mud is not ideal, but under the circumstances there was little choice as the drilling method used was the best the drill crew could do. However the drilling method is ideal if consolidated core samples are to be collected. Generally the use of drilling mud would remove fine grained gold when water is tipped out from the buckets which were used to collect the sludge. As drilling proceeded every six metres, the holes were cased. The length of casings used in each hole varied, to prevent contamination of samples.

SAMPLE PROCESSING Samples collected were split into two portions, one for the archive, and the other to be panned. Panning took place under the bridge of the Naboro Creek. The panned concentrates were then inspected for gold particles using a hand lens and packed in labeled packets. The core samples are to be processed and analysed chemically.

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RESULTS

Five drill holes of depths up to 42.4 m were drilled. Gold grains were found in two panned concentrates from one drill hole. This drill hole is TV00/4 (19-20 m and 20-21 m). Observations of the gold grains under a microscope of 20X magnification showed that the grains are anhedral in shape, suggesting reworking and remobilisation from source. In each of these cases the gold grain was found in coarse sand associated with sub-angular to sub-rounded basaltic gravels of various sizes of up to 1 cm.

CONCLUSIONS The drilling was not a total success in that sample recovery was poor at times. However, drilling confirmed the presence of:

i) gravel beds in the delta plain; and ii) detrtital gold in the area.

1. Despite the poor sample recovery, coupled with bad weather, gold was found in

one of the five drill holes (TV00/4). The gold was found at 19-20 m and 20-21 m depth.

2. The gold grains recovered from the samples are anhedral in shape, suggesting

reworking and remobilisation from source. 3. The methodology of sample recovery and the use of drilling mud is not ideal, but

under the circumstances it was the best option the drilling crew could offer. Generally the use of drilling mud would remove fine gold grains.

RECOMMENDATIONS The fact that gold has been found, despite the drilling not being a total success in terms of sample recovery, warrants further work in the area. Therefore, to determine the extent of detrital gold mineralisation in the area it is recommended that further work be done, to geophysical survey (seismic refraction) to locate buried river channels. Further drilling should be done only if the drilling technique and sample recovery is improved greatly.

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REFERENCES Blatchford, A. 1953. Geology of the Tavua Goldfield, Viti Levu, Fiji. Australasian Institute

of Mining and Matellurgy, Proceedings 168-169:13-51. Cohen, Em. 1962. Revised geology of the Tavua Goldfield, Fiji. Australasian Institute of

Mining and Metallurgy, Proceedings 204:135-160. Ibbotson, P. 1967. Petrology of the Tertiary Caldera, Tavua Goldfield. Fiji Geological

Survey Memoir 3. Setterfield, T.N; Eaton, P.C; Rose, W.J and. Sparks, R.S.J. 1991: The Tavua caldera,

Fiji: a complex shoshonitic caldera formed by concurrent faulting and downsagging. Journal of the Geological Society, London, Vol 148, 1991, pp. 115-127.

preliminary report on detrital gold assessment …

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