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Lone Tree |
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Nevada, USA |
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Au
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Super Porphyry Cu and Au
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The Lone Tree gold deposit is located ~55 km south-east Winnemucca in Humboldt County, Nevada, USA and 11 km NNW of the Marigold mine in the Battle Mountain mining district (#Location: 40° 49' 55"N, 117° 12' 37"W).
The deposit is located towards the northern margin of the Battle Mountain - Eureka Gold Trend which hosts a number of Cu-Mo porphyry and Au skarn deposits, e.g., Buckingham, Copper Canyon, Copper Basin and Elder Creek, as well as sedimentary rock-hosted gold deposits, e.g., Lone Tree, Buffalo Valley, Marigold, North Peak and Trenton Canyon, which have been classified as distal disseminated deposits (Doebrich and Theodore, 1996; Theodore, 1998, 2000; Reid et al., 2010).
For details of the geological setting, see the Battle Mountain - Eureka Trend - Geology record.
The Lone Tree deposit is located between the Roberts Mountain and Golconda thrusts in siliciclastic rocks of the Ordovician Valmy Formation and in the Upper Carboniferous (Pennsylvanian) to Permian Battle Mountain and Edna Mountain Formations, and above the Golconda thrust in siliciclastic and carbonate rocks of the Lower Carboniferous (Mississippian) to Permian Havallah sequence. Ore is also hosted by rhyolitic dykes that were emplaced at 40.95 ±0.06 Ma (zircon U-Pb CA-ID-TIMS; Holley et al., 2019).
Ore is structurally controlled with most mineralisation hosted by brecciated sedimentary rocks in the 50 to 120 m wide, north-trending Wayne zone (Bloomstein et al., 1993, 2000). The faults of the Wayne zone are steeply dipping and have a dominant normal dip-slip displacement. Outside this zone gold is found in subsidiary faults and fractures, which are commonly steeply dipping and strike both NNW and NNE. The Lone Tree pit is elongated north south and is ~2.9 km long and up to 900 m wide (Holley et al., 2019).
Gold is associated with sericitic and argillic alteration of both siliciclastic rocks and dykes and with decarbonatisation and Fe carbonate alteration of the carbonate-bearing units. It is also contained within Fe-As sulphides and fine grained quartz alteration of all rock types. Some 30 to 45% of the deposit has been oxidised, penetrating into the host sequence along numerous steeply dipping north-south, east-west and NNE–SSW structures (Holley et al., 2019).
Gold grades are sympathetic to Ag, As, Hg and Sb levels. Gold grades are highest in quartz-sulphide ore hosted by siliciclastic and carbonatic sedimentary rocks and rhyolitic intrusions. Ore in these hosts comprises fine-grained quartz and sericite intergrown with disseminated sulphide minerals (quartz-sericite-pyrite alteration), constituting weakly mineralised pyrite or marcasite cores surrounded by fuzzy arsenopyrite rims that contain up to ~2000 ppm Au. Lower gold grades are found in late-stage banded pyrite breccias consisting of a finely zoned Au-poor pyrite matrix surrounding jigsaw-fit clasts of quartz, illite, barite and adularia-altered siliciclastic rock. The age of the main-stage mineralisation is bracketed between the emplacement of the dykes (see age above) and an adularia 40Ar/39Ar age of 40.14 ±0.74 Ma (Holley et al., 2019).
Reserve and resource figures published by Newmont for the Lone Tree operation at Dec. 2003 were:
Proven + probable reserves - 16.6 Mt @ 2.63 g/t Au
Measured + indicated resources - 2.1 Mt @ 1.65 g/t Au
Inferred resources - 0.5 Mt @ 1.65 g/t Au
Prior to mine closure in 2006, Santa Fe Pacific Gold and Newmont produced 130 tonnes of gold at an average grade of 2.06 g/t from Lone Tree, primarily from the north-south to NNW-SSE–striking Wayne zone (Holley et al., 2019).
The most recent source geological information used to prepare this decription was dated: 2019.
Record last updated: 2/8/2019
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.
Lone Tree
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Selected References:
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Holley, E.A., Lowe, J.A., Johnson, C.A. and Pribil, M.J., 2019 - Magmatic-Hydrothermal Gold Mineralization at the Lone Tree Mine, Battle Mountain District, Nevada: in Econ. Geol. v.114, pp. 811-856.
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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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