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

Cooke, DR ORCID: 0000-0003-3096-5658, White, N, Zhang, L, Chang, Z and Chen, H 2017 , 'Lithocaps - characteristics, origins and significance for porphyry and epithermal exploration', in Proceedings of the 14th SGA Biennial Meeting: Mineral Resources to Discover , Society for Geology Applied to Mineral Deposits, pp. 291-294 .

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Abstract

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 steeply-dipping 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 Type: Conference Publication
Authors/Creators:Cooke, DR and White, N and Zhang, L and Chang, Z and Chen, H
Keywords: porphyry, copper, gold, lithocap, exploration, geochemistry, mineralogy
Journal or Publication Title: Proceedings of the 14th SGA Biennial Meeting: Mineral Resources to Discover
Publisher: Society for Geology Applied to Mineral Deposits
Copyright Information:

Copyright 2017 Society for Geology Applied to Mineral Deposits

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