mdsg 2016 mgeol poster
TRANSCRIPT
4. Mineralisation style at Enterprise
3. Location
Figure 1: Map showing the location the Munali intrusion, hosted within passive margin rift sediments of the Zambezi Supracrustal sequence of southern Zambia.
Department of Geology, University of Leicester, LE1 7RH, UK, [email protected]
Comparison of the style and nature of breccia hosted Ni-sulphide deposits of the Munali intrusion, Zambia
Chloe L Mitchell and David A Holwell
1. Introduction 2. Project aims The Munali mafic-ultramafic intrusion comprises an unmineralised gabbroic core and a late stage, marginal ultramafic breccia with massive and disseminated Ni-sulphide mineralisation. Multistage emplacement during breccia formation has given rise to multiple styles of sulphide mineralisation which have never been classified. Mabiza Resources’ Enterprise deposit (Fig. 1) contains reserves of 5.8 Mt at 1.02% Ni and has previously been mined [1]. However, the base of the ultramafic intrusion, and any associated feeder conduit, has not been identified.
6. Apatite-oxide and sulphide immiscibility
The abundance of apatite-oxide and Fe-sulphide assemblages in the late stage sulphide phases is unusual in magmatic deposits. Similar textures are recorded in the Babbit sulphides of the Duluth Complex, Minnesota, and are interpreted to represent coexisting Fe-Ti-P rich and sulphide immiscible liquids within the melt [3]. Munali also appears to show evidence for Fe-Ti-P and sulphide liquid immiscibility (Fig. 5).
References
[1] Snowden Mining Industry Consultants, 2012: Final Resource Report, Munali deposit for Albidon Ltd, 39 p.
[2] Barnes, S. J., et al. (2015), The mineral system approach applied to magmatic Ni–Cu–PGE sulphide deposits, Ore Geology Reviews, (in press).
[3] Ripley, E. M., et al. (1998), Evidence for Sulfide and Fe-Ti-P-Rich Liquid Immiscibility in the Duluth Complex, Minnesota, Economic Geology, v. 93, p. 1052-1062.
The Munali ultramafic intrusion likely represents a conduit-hosted Ni-sulphide deposit which shows evidence for the following:
Underground mapping of the Enterprise deposit reveals the chaotic nature of the orebody; sulphides form the matrix to a mega-breccia which incorporates mafic-ultramafic clasts (Fig. 3). Relative timings of sulphide injections have been determined from crosscutting relationships. Multiphase sulphide injection may represent cycles of deposition, downward re-injection, re-entrainment and re-deposition operating within the vertically extensive magma conduit [2].
The aims of this project are to:
• Provide the first detailed underground
mapping of the Enterprise deposit to
determine relative timings of sulphide
styles.
• Classify the sulphide styles in terms of
mineralogical and textural characteristics
• Vector towards the location, and
determine the morphology of, any feeder
conduits which may be associated with
the ultramafic intrusion.
3-Dimensional modelling illustrates the morphology of the ultramafic intrusion and may indicate a potential feeder zone situated beneath the Enterprise deposit (Fig. 2).
5. Classification of sulphide styles 7. Conclusion
1. Interstitial sulphide
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b)
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Cr V Se As Sb Mo W Pb Sn Zn Sr Y La Ce Nd0.001
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Cr V Se As Sb Mo W Pb Sn Zn Sr Y La Ce Nd
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2. Talc-carbonate sulphide 3. Massive sulphide 4. Apatite sulphide 5. Calcite sulphide
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Cr V Se As Sb Mo W Pb Sn Zn Sr Y La Ce Nd
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Talc-carbonate altered ultramafic
py po-py
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dunite clast ccp cc
interstitial po mag po-pn
Moderate Y, Sr, La, Ce, Nd associated with minor apatite.
High Y, Sr, La, Ce and Nd associated with apatite
Low Y, Sr and La
Low Y, Sr and La Variable Y, Sr and La
Figure 4: a) Examples of the five sulphide styles. b) Mantle normalised multi-element plots for each sulphide style.
The Munali sulphide assemblage is po >> pn > cpy ± py. Five sulphide styles have been identified based on mineralogical, textural and geochemical characteristics (Figs. 3 and 4a-b).
1. Multiple injections of sulphide,
2. The potential for further mineralisation at depth associated with a feeder conduit beneath Enterprise,
3. The presence of an early immiscible sulphide liquid which gave rise to the massive and talc-carbonate sulphide phases,
4. The presence of a late stage, immiscible Fe-Ti-P liquid which gave rise to the apatite-magnetite sulphide phase.
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Figure 5: Reflected and transmitted light photomicrographs showing euhedral apatite within the Munali and Babbitt sulphides.
MUNALI SULPHIDES BABBITT SULPHIDES MUNALI SULPHIDES BABBITT SULPHIDES [3] [3]
Figure 3: Geological map of an underground crosscut through the orebody at Enterprise. Orebody dips steeply to the SW.
NW SE
Footwall gabbro 4 m
to left
Hanging wall meta-sediments
8 m to right
Figure 2: 3D modelling using geological intersection data from deep drillcores.
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FEEDER CONDUIT
PROSPECTIVE FEEDER CONDUIT