Cortez Hills underground, Cortez Mining District, Lander County, Nevada, USAi

Regional Level Types
Cortez Hills underground	- not defined -
Cortez Mining District	Mining District
Lander County	County
Nevada	State
USA	Country

Carlin type gold deposit in breccia
Structure: The deposit lies within the Cortez Window of the Roberts Mountain Thrust (Cortez Range). The deposit occurs within the Cortez Window in the Roberts Mountain Thrust.

Alteration: Host rocks have been decalcified, silicified, leached, bleached, argillized, and oxidized. This phase of low grade hydrothermal alteration occurred after intrusion of the porphyry sill, and removed most of the carbon. A decalcification halo extends into the host rock surrounding the mineralized area. Mineralization is associated with silicification. Pervasive oxidation and marble development are key alteration types associated with gold deposition

Tectonics: The upper portion of the Devonian carbonate sequence beneath the Roberts Mountains thrust hosts the Cortez Hills deposit.

Commodity: Commodity Info: Gold is submicroscopic (micron to submicron-sized particles of native gold), occurring in minute specks of arsenian pyrite. Ore Materials: native gold, pyrite Gangue Materials: hematite, goethite; gangue: quartz, carbonate, clays

Deposit: The recent Cortez Hills discovery is the result of focused exploration efforts along an extensive high-angle fault corridor that localizes the distribution of gold in the Cortez area. Projection of this structural corridor under cover, coupled with gravity data, were the key exploration techniques that led to the discovery of Cortez Hills. Gold is localized where limestone was faulted, brecciated and folded along margin of Tertiary intrusive, gold is micron-to sub-micron-size. The upper portion of the Devonian carbonate sequence beneath the Roberts Mountains thrust hosts the Cortez Hills deposit. Pervasive oxidation and marble development are key alteration types associated with gold deposit. The Cortez Hills deposit is hosted in the upper portion of the Devonian carbonate sequence. It has a strike length of more than 300 m and is approximately 200 m wide. The mineralized zone starts approximately 120 m below surface and continues up to 460 m. The deposit remains open with expansion potential evident to the west and at depth.

Deposit type: Sediment-hosted Au

Development: Placer Dome is the operator and owner of a 60% joint venture interest in the Cortez Joint Venture (CJV). The remaining 40% is held by Kennecott Explorations (Australia) Ltd. The recent Cortez Hills discovery is the result of focused exploration efforts by CJV staff along an extensive high-angle fault corridor that localizes the distribution of gold in the Cortez area. Projection of this structural corridor under cover, coupled with gravity data, were the key exploration techniques that led to the discovery of Cortez Hills. June 2004, Placer announced that they had drilled a hole in the area between the Cortez Hills and the Pediment deposits that had returned 1.5 ounces per ton over more than 400 feet.

Geology: The deposit is also associated with the Horse Canyon volcanics (andesite flows, rhyolite plug) and the Roberts Mountain Limestone (silty, argillaceous, carbonaceous, pyrite-bearing limestone).

Ore(s): Gold is localized where limestone was faulted, brecciated and folded along the margin of a Tertiary intrusive.

Other Databases

Link to USGS MRDS:	10310435

Other Regions, Features and Areas containing this locality

References