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.