System type: Carlin-type, sediment-hosted gold
Target: Structurally-controlled mineralization with disseminated halo
The Larus project contains a sediment-hosted (Carlin-type) gold system along the Cortez gold belt in central Nevada. The project is 23 miles northwest of Eureka, site of Barrick Gold Corp’s Ruby Hill gold mining operations, 30 miles southeast of Barrick’s Cortez Hills gold mining operations, 2 miles northwest of the Mt. Hope molybdenum deposit and 6 miles east of the Gold Bar district.
Larus lies along the eastern “leading” edge of the Roberts Mountains allochthon, a regional package of deep-water siliciclastic rocks (western facies, upper plate) that were thrust generally eastward over a platform carbonate sequence (eastern facies, lower plate) in Late Devonian to Early Mississippian time. Within the project, a block of lower-plate Devonian limestone, about 1 km by 0.5 km in outcrop area, is underlain by upper-plate siliciclastics (Vinini Fm, Ov) and locally Early Tertiary volcanics. A detachment fault (relatively low-angle normal fault or gravity slide) separates the limestone from the underlying upper-plate and volcanic rocks. A zone of megabreccia containing blocks of limestone, Ov and felsite occurs along and subjacent to the detachment. North-northwest (N-NW) trending high-angle faults cut the detachment producing a N-NW-trending graben of limestone. In the limestone block, gold mineralization occurs within silicified limestone (jasperoid) which commonly contains stockworks of quartz veins. The jasperoids and veins commonly display, steep, N-NW-trending fabrics and are coincident with N-NW-trending high-angle faults that also cut the detachment and control the outcrop pattern of the limestone block. Blocks of Ov shale and limestone are locally silicified and mineralized within the megabreccia, and N-NW-trending weakly-mineralized silicification also occurs at one location within the underlying felsite. Preliminary sampling has returned significant gold in several widely-spaced areas, with values reaching 3.23 ppm (g/t) gold in a stibnite-bearing quartz vein adjacent to jasperoid, 1.16 ppm in jasperoid lacking abundant quartz veins and 2.04 ppm in silicified Ov shale. In addition to stibnite, minor tetrahedrite is locally present in quartz veins. Mineralization is known over a strike length of at least 4,000 feet (1,200 m) and a vertical range of at least 515 feet (157m). A N-NW trending altered felsic dike intrudes Ov on the south side of the limestone block and is parallel to the N-NW faults that localize silicification and cut the detachment fault.
As detailed mapping and previous drilling indicate that mineralization occurs along N-NW-trending faults that cut the detachment fault, mineralization occurred after the limestone was emplaced and is locally rooted. This N-NW fabric is the same structural control to gold mineralization in productive Carlin-type gold deposits along the Cortez gold belt, including in the Pipeline - Cortez Hills - Goldrush district (+50 million ounces). The Larus project also lies along a N-NW-trending regional magnetic linear which passes through the small Chert Cliff gold deposit about 6 miles to the northwest.
Historic exploration drilling prior to 1990 was largely shallow (<400 feet) and was aimed at discovering, stratiform, replacement-style mineralization as opposed to testing the N-NW mineralized structural zones with angle drilling. There has been no significant work at the project since 1990. It is recommended that deep (~1,500 feet) angle holes be completed across the principal N-NW-trending fault zones to assess mineralization to depth.
Regional geologic map showing the locations of significant gold deposits in black and the location of the Larus Project and Mount Hope Molybdenum deposit (outline of ultimate open pit); white dotted lines are linear magnetic features in the Larus area.
Looking south at N-NW-trending (350o), steeply west-dipping jasperoid breccia cutting limestone (333 ppb Au).
Silicified Ov black shale from megabreccia below detachment fault 1.495 ppm).