The Goldstrike property is underlain by strongly deformed Paleozoic strata overlain unconformably by relatively flat-lying Tertiary sedimentary and volcanic rocks ranging from Paleocene to Miocene in age. Some parts of the property are covered by thick alluvial deposits.
Paleozoic strata range from Devonian to Permian in age and generally reflect deposition of carbonate and clastic strata in shallow, inner shelf tide flat and lagoon settings. Major stratigraphic units include the Mississippian Redwall Limestone, Chainman Shale and Scotty Wash Sandstone, the Pennsylvanian Callville Limestone, and the Permian Pakoon Dolomite and Queantoweap Sandstone. Mesozoic strata are exposed locally in the southern and eastern part of the property and include the Jurassic Navajo Sandstone and Cretaceous Grapevine Wash Formation.
Paleozoic and Mesozoic strata were subject to southeast-vergent folding and thrust imbrication during the Cretaceous Sevier orogeny. Mesozoic strata are exposed locally below the Square Top Mountain thrust fault. A thick sequence of conglomerate (Grapevine Wash Formation) was shed southward off the highland formed by thrust faulting.
Tertiary rocks overlie older rocks along a profound unconformity, and include the Paleocene to Oligocene Claron Formation and overlying Miocene Quichapa Group flows and tuffs. The basal Claron Formation consists of conglomerate and sandstone of variable thickness, overlain by conglomeratic limestone. Above the Claron Formation lies a sequence of interlayered limestone and tuff, followed by a thick sequence of Miocene volcanic rocks. Tertiary rocks dip gently to moderately to the north, and are cut by abundant high- to moderate-angle oblique faults that generally strike either ENE or WNW. In the vicinity of the Goldstrike mine, faulting has resulted in the formation of several arcuate graben structures.
Alteration and mineralization consist largely of finely disseminated gold hosted in silicified or jasperoidized rocks in the basal Claron Formation conglomerate and underlying Paleozoic carbonate rocks, and along high-angle faults. Silicification is accompanied by clay alteration, iron oxides and decalcification of limy host rocks. Rare sulphide mineralization, consisting of finely disseminated arsenical pyrite, is noted in a few drill holes. Altered and mineralized zones are characterized by elevated As, Sb and Hg. Gold shows a strong spatial association with ENE, NE and NW-striking high angle faults. In the eastern part of the mine trend, mined deposits were generally tabular in shape and gently north dipping along the basal Claron contact. In the western part of the mine trend, deposits were steeply dipping tabular bodies developed along fault zones and steeply-dipping bedding planes, partially or entirely within Paleozoic strata. Overall, the alteration and geochemistry are similar to sediment-hosted “Carlin style” systems associated with Paleozoic carbonate strata in eastern Nevada and western Utah.
Surface exposures of the mineralized basal Claron unconformity were the primary target for previous operators and were well tested by drilling and later mining. However, in many areas this unconformity lies under shallow volcanic cover in small graben structures, in some cases immediately adjacent to historic pits. These areas, as well as down-dip extensions of faults, form the primary targets for discovery of additional gold mineralization.