Gold Mineralization at the Golden Trail Project, Northeastern Elko County, Nevada

摘要

The Golden Trail Project is located along the northeastern margin of the recently identified Long Canyon trend in eastern Nevada, a region of Paleozoic strata that were strongly and complexly deformed by mid-Mesozoic orogeny and host major gold deposits. Golden Trail is a sedimentary, rock-hosted, precious metals exploration prospect about 60 kilometers north of Wells, Nevada, in the eastern Knoll Mountains. Gold mineralization overprints zones of early, locally variable, calcsilicate skarn and hydrothermally altered limestone. Late precious metal veins, replacement zones, and mineralized breccias host the highest gold values. Host rock lithostratigraphy includes near horizontal bedded shallow marine sediments of the Middle Permian Pe-quop Formation that structurally overlie but are older than highly carbonaceous sedimentary rocks that are likely part of the Permian Meade Member of the Phosphoria Formation. The overthrust lithologies include fossiliferous limestone, siltstone, sandstone, and conglomerates. Fossil hash beds and clastic sediments are locally poorly sorted and suggest shallow water dynamic deposition. Underlying younger sediments are phosphate-rich and highly carbonaceous lithologies that include thinly-bedded shale, siltstone, mudstone, chert and minor limestone. In the project area, gold is most abundant within zones of hematitic, multiphase, dissolution breccia controlled by northwesterly striking faults, joints, bedding planes, and favorable porous lithology. Silicification is common to all areas of gold mineralization, but highest values locally occur adjacent to iron oxide-rich jasperoids which, themselves, typically contain lower gold values. Gold mineralization is late and generally centered on approximately 10 square kilometers of thermal metamorphism, and hydrothermal/metasomatic alteration. Gold and base metal mineralization occurs locally in northwest-striking dilational zones containing numerous, high-angle gold-bearing veins and adjacent replacement zones, and centered within calcsilicate skarn. The largest of these, the Golden Trail Vein (GTV), cuts calcsilicate hornfels, marble, and hydrothermally altered limestone central to, and contiguous with, a strong northwest striking gravity high. The GTV extends over 1,200 meters in length with an associated alteration zone averaging 30 meters wide. Gold values above 20 ppb are common with several samples assaying above 9 g/t Au and one above 28 g/t Au. A continuous 1.5 meter channel sample assayed over 13 g/t Au. In weathered and oxidized outcrop samples, elevated Ag, As, Sb and T1 values accompany Au in iron-rich zones commonly with a carbonate+montmorillonite+white mica assemblage. Mineralization at the Golden Trail Project is similar in geologic setting, host rock lithology, alteration and gangue mineralogy, and geochemistry to sedimen- tary rock-hosted gold deposits and especially gold mineralization typical of eastern Nevada, including the Carlin-type Long Canyon gold deposit in the Pequop Mountains.