Lithocaps – characteristics, origins and significance for porphyry and epithermal exploration

Cooke, David R., White, Noel C., Zhang, Lejun, Chang, Zhaoshan, and Chen, Huayong (2017) Lithocaps – characteristics, origins and significance for porphyry and epithermal exploration. In: Proceedings of the 14th Biennial SGA Meeting (1) pp. 291-294. From: 14th Biennial SGA Meeting, 20-23 August 2017, Quebec City, Canada.

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Lithocaps are subsurface, broadly stratabound alteration domains that are laterally and vertically extensive. They form when acidic magmatic-hydrothermal fluids react with wallrocks during ascent towards the paleosurface. Although lithocaps typically have steeplydipping structural roots, there is a significant component of lateral fluid flow involved in lithocap formation, either through permeable aquifers and/or a well-developed fracture mesh. Lithocaps can have lateral dimensions greater than 10 km and thicknesses of more than 1 km. In ancient settings, partially eroded lithocaps are typically exposed as silicified ridges and cliffs. These features do not mark the original paleosurface – instead they are erosional remnants of what was once an extensive subsurface alteration domain that may have been capped by low temperature argillic- and/or propylitic-altered rocks. High sulfidation state mineralisation typically occurs in silicicaltered rocks within lithocaps, either as stratabound replacements, veins and/or breccia cement. The quartz-rich mineralized domains can produce a resistivity high. Pyrite is ubiquitous in lithocaps prior to weathering, and can yield complicated chargeability responses, some of which may be associated with mineralization. The alteration assemblages are invariably magnetite-destructive, and can obscure the magnetic signature of an underlying porphyry deposit. Combining SWIR and whole rock geochemistry can provide effective vectoring tools within lithocaps.

Item ID: 51862
Item Type: Conference Item (Presentation)
ISBN: 978-2-9816898-0-1
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Date Deposited: 23 May 2018 01:31
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040307 Ore Deposit Petrology @ 100%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840105 Precious (Noble) Metal Ore Exploration @ 50%
84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840102 Copper Ore Exploration @ 50%
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