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Rincon del Tigre Layered Mafic Intrusion |
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Bolivia |
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PGE PGM Pd Pt Au Cu V
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Super Porphyry Cu and Au
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The Neoproterozoic Rincón del Tigre Complex layered mafic-ultramafic intrusion, which contains concentrations of platinum group elements, gold, copper, magnetite and vanadium, is located in the lowlands of far eastern Bolivia.
The 990 Ma, 4.6 km thick complex is exposed over an area of 60 x 27 km as an open, gently south-east plunging syncline-anticline fold couple before passing beneath later cover rocks to the north and east. It was intruded along the slightly disconformable contact between the quartzites of the Sunas Group and the overlying Vibosi Group sandstone and arkose.
The complex comprises, from the base:
1). A lower 3 km thick ultramafic unit, essentially composed of multiple repetitions of dunite to olivine-bronzitite to bronzitite each only a few metres thick.
2). A middle 1.5 km thick mafic unit, comprising a basal norite overlain by gabbro and then magnetite gabbro. Copper dominant concordant disseminated sulphide mineralisation was recognised in the magnetite-gabbro, underlain by a zone of precious metals.
3). An upper 0.75 km thick felsic unit composed mainly of massive granophyre.
The layered ultramafic and mafic units have been together alternatively subdivied on petrological grounds into:
The Basal Unit - which is 400 to 900 m thick, comprising a variable sequence and distribution of litholologies and is characterised by fine grained bronzite- and plagioclase-rich lithologies, massive poikilitic biotite rich, granular harzburgite-olivine bronzitite and massive finely layered granular harzburgite-olivine bronzitite. The proportion of orthopyroxene and plagioclase increases upwards. The basal unit is locally capped by around 40 m of complexly layered, fine- to medium-grained granular harzburgite-olivine bronzitite, bronzitite, norite and anorthosite.
Unit 1 - which is up to 625 m thick and is everywhere composed of a series of poikilitic to granular harzburgite. Many of the layering units in the upper part include modally layered olivine bronzitite at the top.
Unit 2 - begins with 420 to 500 m of layered poikilitic to granular harzburgite, with localised chromitites near the base. The harzburgite is overlain by the main 40 to 80 m thick bronzitite layer with well developed augite oikocrysts and minor olivine. The main bronzitite is overlain by an 865 to 1170 m thick succession of mafic rocks, separated by a variable pegmatoid zone before 80 m of olivine bearing norite with irregular, up to 15 cm thick, lenses of anorthosite near the base. The norite grades up into a gabbro, where 195 to 350 m above the base of the mafic suite titaniferous magnetite joins plagioclase, augite and bronzite above a sharp contact to form a magnetite gabbro. The magnetite-gabbro at 820 m is the thickest unit in the complex. In the more magnetic zones the gabbro contains 5 to 10% magnetite with associated 0.08 to 0.12% vanadium.
The Precious Metal zone of the complex is associated with the magnetite gabbro and occurs as a persistent zone of low grade sulphide and precious metals 80 to 185 m thick. The Precious Metals zone comprises an upper copper sulphide rich portion (with 0.07 to 0.22% Cu) commencing with the lowest sulphides at 23 to 70 m above the first appearance of significant magnetite. The precious metals interval, the lower part of which straddles the base of the magnetite zone occurs below the copper zich band. The individual precious metals are found in separate sulphide poor sub-zones, each of which is several tens of metres thick in the order upwards of Rh to Pt to Pd to Au. Maximum precious metal values in 1 m intervals were 1.8 g/t Pd, 0.68 g/t Pt, 0.35 g/t Au
The mineralisation is sub-economic.
For more detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2000.
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.
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Selected References:
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Prendergast M D 2000 - Layering and precious metals mineralization in the Rincon del Tigre Complex, eastern Bolivia: in Econ. Geol. v95 pp 113-130
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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, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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