PIMS - Porphyry Indicator Minerals from Alkalic Cu-Au Porphyry Deposits in British Columbia
(NTS 092H, 092A, 093N)
- Farhad Bouzari, Mineral Deposit Research Unit, UBC

The common occurrence of resistate minerals in mineralized and altered portions of British Columbia's alkalic porphyry copper deposits suggest that these minerals may be utilized as indicators of mineralization, especially in terrains covered by glacial till. A recent Geoscience BC supported MDRU project (Geoscience BC Report 2011-17) demonstrated the unique physical and chemical characteristics of porphyry indicator minerals (PIMS), particularly apatite, in alkalic and calc-alkalic porphyry deposits in BC, and suggested potential applications of other resistate minerals such as garnet, magnetite, titanite and diopside. This project, therefore, aims to study those resistate minerals that are directly associated with alkalic porphyry deposits in order to establish specific criteria that will result in their application in the exploration of concealed deposits in BC.

PIMS are chemically stable in weathered environments, heavy, sufficiently coarse-grained and display characteristic features that can directly link them to a porphyry related alteration assemblage. These minerals commonly display unique physical properties such as color, size and shape that allow their presence to be used as a prospecting tool in a similar manner to which kimberlite indicator minerals (KIMS) are used. Moreover, the chemical compositions of PIMS can identify mineralizing environments that relate directly to specific alteration zones in porphyry systems. Although easy to collect in heavy mineral concentrates, these minerals have rarely been used as exploration tools. Therefore, by evaluating the presence, abundances, relative proportions, and compositions of PIMS from surficial materials, it is possible to follow-up geophysical and geochemical anomalies to vector towards concealed porphyry copper deposits in highly-prospective terrains such as Quesnel and Stikine in central BC.

The purpose of this project is to identify the occurrence, types, relative amounts and compositions of selected PIMS in several porphyry deposits in order to elucidate important PIMS signatures. Therefore, PIMS signature in Copper Mountain, Mt. Polley, Mt. Milligan and Lorraine alkalic porphyry deposits will be characterized in order to evaluate their signatures in proximal tills, stream sediments, and heavy mineral concentrates.

Posters and Presentations
2013: PIMS - Porphyry Indicator Minerals from Alkalic Porphyry Cu-Au Deposits in British Columbia
- Mineral Exploration Roundup Conference Poster (pdf, 9.1 MB)
Technical Articles
2013: "Porphyry indicator minerals (PIMs) from alkalic porphyry copper-gold deposits in south-central British Columbia"
- Summary of Activities 2012, Report 2013-1 p. 37-46 (pdf, 3.6 MB)
2014: "Petrographic characteristics of porphyry indicator minerals from alkali porphyry copper-gold deposits in south-central British Columbia"
- Summary of Activities 2013, Report 2014-1 p. 53-62 (pdf, 4.7 MB)
Final Deliverables

Journal Article - Economic Geology
Hydrothermal Alteration Revealed by Apatite Luminescence and Chemistry: A Potential Indicator Mineral for Exploring Covered Porphyry Copper Deposits - Farhad Bouzari, Craig J.R. Hart, Thomas Bissig, Shaun Barker Economic Geology Sep 2016, 111 (6) 1397-1410; DOI: 10.2113/econgeo.111.6.1397

M.Sc. Thesis - A. Celis
TITANITE AS AN INDICATOR MINERAL FOR ALKALIC PORPHYRY CU-AU DEPOSITS IN SOUTH-CENTRAL BRITISH COLUMBIA - University of British Columbia, 2015 - Available digitally through UBC (pdf, 36.5MB)

Abstract: Exploration success in large parts of the Quesnel and Stikine terranes in south-central British Columbia (BC) has been limited due to extensive coverage by glacial sediments (Ward et al., 2009), where traditional geophysical and geochemical exploration methods have proven to be limited or impractical (Gent et al., 2011). The occurrence of resistate minerals such as apatite, epidote, garnet, magnetite, rutile and titanite as alteration products in porphyry deposits suggests that they could be utilized as porphyry indicator minerals (PIMs) to provide a new tool to increase exploration success in covered terrains (Bouzari et al., 2011).

Titanite (CaTiSiO5) is a common accessory mineral in alkalic Cu-Au porphyry deposits that is known to record various magmatic and hydrothermal processes in its texture and chemical composition (). In this research, titanite hosted in bedrock from the Mount Polley, Mount Milligan and Copper Mountain alkalic porphyry Cu-Au deposits of south-central BC, as well as in surrounding till sediments, was characterized based on petrography, heavy mineral separation, and Electronic Microprobe (EMP) and Laser Ablation Inductively Coupled-Plasma Mass Spectrometry (LA-ICP-MS) chemical analyses. The main objective is to determine key diagnostic features of titanite that are related to alkalic porphyry alteration and mineralization.

Titanite typically forms as replacement of mafic minerals, such as augite, biotite and magnetite during K-silicate and Na-Ca alterations. Thus, four types of titanite were defined based on key petrographic and chemical features: primary magmatic (MAG), metasomatic (MET), secondary (SEC) and altered (ALT) titanites. MAG titanite is typically euhedral, colourless, exhibits concentric compositional zoning and has intermediate (1-1.5) Fe/Al ratios, low V and F, high REE (Σ REE = 5000 -7000 ppm), high HFSE (Y, Nb, Ta, Th/U) and REE patterns with LREE convex upwards and strong negative Eu anomalies. MET titanite has euhedral to subhedral habit, distinctive caramel brown colour, abundant microfractures, amorphous high contrast zoning, and is chemically similar to MAG titanite but has higher concentrations of REE and HFSE (Y, Nb, Ta, Th/U). SEC and ALT titanites are typically blond to honey brown colour and exhibit anhedral habit with fine cavities, dissolved edges, patchy/sector compositional zoning and significant degree of rutile replacement. Chemically, they have low (< 1.0) Fe/Al ratios if affected by Na-Ca alteration, high (> 1.5) Fe/Al ratios if affected by K-silicate alteration, V enrichment when texturally associated with Cu mineralization and are typically depleted in REE (Σ REE < 5000 ppm) and HFSE. Titanite recovered from till sediments near studied alkalic deposits preserve the texture and chemical signatures obtained in the rock, despite surficial weathering. Therefore, the above classification of titanite constitutes a useful mineralogical tool for exploration for alkalic Cu-Au porphyry deposits in covered terrains.

 


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