Pony Creek prospect, Larrabee Mining District, Elko County, Nevada, USAi

Regional Level Types
Pony Creek prospect	Prospect
Larrabee Mining District	Mining District
Elko County	County
Nevada	State
USA	Country

Structure: Pinyon Range Anticline and Pinyon Graben The Pony Creek/Elliot Dome Project lies within the southern extension of the Carlin Trend, along the axis of Pinyon Range Anticline, paralleling the crest of the Pinyon Range. The Project area lies within a zone of convergence of two major structural trends which are the boundaries of a north-south series of grabens and half-grabens collectively referred to as the Pinyon Graben. Both the Pinyon Range Anticline and Pinyon Graben are estimated to be of late Mesozoic age.

Alteration: Alteration within the rhyolite intrusive is characterized by quartz-sericite-pyrite mineralization associated with north and north-east-trending faults. The shear zones are fragmental and/or brecciated, containing very fine-grained quartz, sericite, and pyrite or limonite. Pyrite occurs secondary in fractures. Away from the shear zones the rhyolite gradually becomes fresher, grading outward from a rock with relict feldspar ghosts to one with a distinct porphyritic texture. In the center of the intrusion the rocks have a granular texture in which the feldspars have been altered, leaving open, clay-filled vugs. ?Sanded rhyolite? and ?rhyolite sand? are terms used by Newmont to describe a unique texture of the rhyolite often occurring in mineralized areas. The sanded rhyolite consists of medium-grained rounded clasts of glassy rhyolite breccia occurring near the margins and at the base of the intrusive. Sediments along the margins of the rhyolite intrusive and immediately beneath it have been silicified, decalcified and sulfidized. In and around the mineralized cells, the sediments have been extensively oxidized (hypogene).

Tectonics: The Paleozoic geology is dominated by the Antler Orogeny. Mountain building during this period resulted in the formation of a high mountain range to the west of central and eastern Nevada. Erosion of the mountains resulted in the covering of most of central and eastern Nevada with a large clastic wedge composed of conglomerate and coarse sandstone to the northwest and fine sandstone, siltstone and shale to the southeast. In addition to the folding and low-angle faulting commonly associated with orogenic compression and mountain building, high-angle reverse fault and strike-slip faulting were widespread in response to the Antler and later orogenies in central and eastern Nevada. Important wrench fault systems were formed sometime during this period. The gold deposits found along the Carlin Trend are believed to be related to a northwest trending wrench fault that was active as early as the Jurassic era, moving at the time in a left-lateral sense. These high-angle faults are critical to localizing the fluid flow responsible for the deposition of gold deposits in central and eastern Nevada.

Commodity: Ore Materials: gold Gangue Materials: marcasite, pyrite, minor realgar and stibnite. Quartz, sericite, pyrite and limonite.

Deposit: All significant gold mineralization outlined to date on the Pony Creek Property appears to be directly related to felsite breccias formed within a rhyolite intrusive. Over 90% of the mineralization on the property lies within 500 feet of the surface and occurs primarily along north and north-east trending structures within the rhyolite intrusive body and in silicified and altered Mississippian to Permian clastic rocks immediately beneath and adjacent to the intrusive. Gold mineralization is directly related to felsite breccias formed within the rhyolite intrusive body either by phreatomagmatic processes, faulting, or both. Over 90% of the mineralization on the property lies within 500 feet of the surface and occurs primarily along north and north-east trending structures within the rhyolite intrusive body and in silicified and altered Mississippian to Permian clastic rocks immediately beneath and adjacent to the intrusive. Mineralization in the southern portion of the Pony Creek claim boundary (known as the Bowl area) is located within the southern lobe of the rhyolite intrusive and consists of an assemblage of marcasite and pyrite with minor realgar and stibnite. Two continuous zones of mineralization have been recognized within the Bowl area. The first is a tabular mineralized zone. Presumed to be flat-lying, this zone occurs near the base of the felsite body. The second zone occurs in a steeply dipping, north-trending structure. Gold mineralization is developed along fractures and disseminated in permeable zones in the intrusive and in the matrix of felsite breccias. Past drilling completed by Newmont has indicated that gold in the Bowl area occurs within a large cell of alteration approximately 5,000 feet long by 2,500 feet wide, containing widespread low-grade gold mineralization in the 0.010 to 0.045 ounce per ton range.

Deposit type: Epithermal vein, Comstock

Development: Mineral exploration in southwest Elko County has been occurring since the late 1850s when various prospectors, on their way to the California gold fields, passed through Nevada. In 1869, silver, gold, copper, lead and zinc were discovered 13 miles to the north of the Pony Creek/Elliot Dome Project in the Railroad mining district. This district was worked heavily for copper, lead and silver through the late 19th century and into the early 20th century, with an estimated US$4.7 million in lead, copper, silver, gold and zinc being produced between 1869 and 1968.In 1980, during a search for additional gold deposits along the Carlin Trend, Newmont completed a regional stream sediment sampling program, which returned anomalous gold and arsenic values associated with a large, rhyolitic intrusive igneous body on what is now the Pony Creek Property. Newmont subsequently located 100 claims to cover the prospect during the same year and added a further 80 claims in 1982 to cover additional ground in the Property area. Following the completion of over 50,000 feet of drilling between 1981 and 1989, Newmont outlined a significant gold resource on the Pony Creek Property located within 500 feet of the surface, hosted by the rhyolite intrusive and silicified Mississippian to Permian sediments located immediately beneath and adjacent to the intrusive. Newmont estimated the gold resource in the Upper and Lower Bowl areas (the southern portion of the claim boundary) to be 1.124 million tons grading 0.058 ounces per ton, for approximately 65,000 ounces of contained gold . This estimate did not include any additional mineralization outside of the Bowl area. Newmont continued to explore the Pony Creek Property up until 1990 when they entered into a joint venture agreement with Westmont Mining, Inc. Since 1980, approximately US$5.0 million has been spent on exploration of the Pony Creek/Elliot Dome Project, during which time a number of different companies have completed exploration and development work on the Project. In July 2003, the Pony Creek Property was acquired by Mill City. A document outlining the Property?s gold potential prepared by the company in March 2004, resulted in the calculation of new resource estimates for gold mineralization known to occur over an area of 2.4 miles long by 2,000 to 4,800 feet wide ? an area well beyond the Bowl area mineralization. Based on available data, an inferred gold resource of 32.4 million tons at a grade of 0.044 ounces of gold per ton was calculated, equivalent to 1.43 million ounces of contained gold. Based on the known geologic and grade continuity of this type of deposit in north-central Grandview Gold Inc. has the option to earn a 60% interest in the Pony Creek/Elliot Dome Project (the ?Project?) located in the southern extension of the Carlin Trend. Since 1980, approximately $5.0 million has been spent on exploration of the Pony Creek Project. Past work conducted by companies including Newmont, Barrick, Uranerz and Homestake has included stream sediment sampling, soil sampling and geochemistry, mapping, geophysical surveys, data compilation and analysis and RC drilling. A total of 175 drill holes (95,511 feet) have been drilled on the Pony Creek Property to date. From 167 drill holes, for which information is available, 88 drill holes (50.3%) have gold intercepts of at least 5.0 feet grading 0.010 ounces of gold per ton. Grandview Company believes that, based on the geologic setting at Pony Creek, considerable potential exists for the identification of additional resources at depth, below the 500 foot level.

Geology: Most of the Pony Creek Project is underlain by the Mississippian Webb Formation, which was thrust into current position by the Roberts Mountains Thrust Fault, overlying the Devonian Devils Gate Limestone but underlying the Diamond Peak and Chainman Shale Formations. The Webb Formation, consisting primarily of siliceous mudstone and calcareous siltstone, is the primary host rock for gold mineralization in the South Pinyon Range (as it is at the Rain, South Bullion and Trout Creek deposits. The Webb Formation remains untested at the Pony Creek/Elliot Dome Project. Middle to upper Devonian carbonate rocks through Permian clastic sedimentary are exposed at surface through the Pony Creek Property. Within the Pinon Graben, the south-plunging Pinon Range Anticline exposes progressively older units toward the north. Also within the Graben is a north-south trending, elongate rhyolite porphyry intrusive body of probable Eocene age. This sill-like body, which has intruded the Palaeozoic aged sedimentary rocks along the axis of the Pinyon Range Anticline, is composed of two lobes and contains rocks that have been variously described as rhyolite, felsite or felsic porphyry. Older, Tertiary sedimentary rocks of Palaeocene to Eocene age, composed of conglomerate, sandstone, siltstone and limestone are found to the northeast of the Pony Creek/Elliot Dome Project area.

Ore(s): Ore mineralization is associated with brecciated shear zones.

Other Databases

Link to USGS MRDS:	10310335

Other Regions, Features and Areas containing this locality

References