California, USA

Main commodities: Au
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The Picacho gold deposit, located in south-eastern-most California, USA, and is a low-grade gold deposit in a nearly flat-lying, Oligocene age fault of regional extent.

The deposit is hosted by intensely fractured and faulted Mesozoic leucogranite and by chloritic augen gneiss and schist. It is unconformably overlain, and in fault contact with, unmineralised late Oligocene Quechan volcanic rocks. The deposit is structurally characterised by low to high angle normal and normal-oblique faults at shallow depths in the mine. These faults merging downward with a synchronous, low angle ore-stage extensional faults (the Chocolate Mountains/Gatuna Fault) of probable Oligocene age in deeper portions of the deposit.

This main-stage mineralisation is represented by quartz, pyrite, and specular hematite, accompanied by silicification and sericitization. Gold bearing ore-stage pyrite was formed late in the fault evolution, most likely by mixing of reducing ore fluid with relatively oxidized main-stage fluid during regional Oligocene extension on the Chocolate Mountains/Gatuna Fault.

The Picacho deposit is characterised by a Au-As-Sb geochemical signature consistent with bisulfide complexing of gold in reducing fluid. Miocene normal faults with a wide range of dips over print the deposit, with associated red earthy hematite precipitation, pyrite oxidation, and supergene enrichment of gold.

Between 1981 and 2000 the mine produced 12 tonnes of recovered gold.

The most recent source geological information used to prepare this summary was dated: 2005.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Liebler G S,  1988 - Geology and gold mineralization at the Picacho mine, Imperial County, California: in Schafer R W, Cooper J J, Vikre P G (Eds), 1988 Bulk Mineable Precious Metal Deposits of the Western United States Geol Soc of Nevada, Reno,    pp 453-472
Losh S, Purvance D, Sherlock R and Jowett E C  2005 - Geologic and geochemical study of the Picacho gold mine, California: gold in a low-angle normal fault environment: in    Mineralium Deposita   v40 pp 137-155

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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