McLaughlin Mine (Manhattan Mine), Knoxville, Knoxville Mining District, Napa County, California, USAi

Regional Level Types
McLaughlin Mine (Manhattan Mine)	Mine
Knoxville	- not defined -
Knoxville Mining District	Mining District
Napa County	County
California	State
USA	Country

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A former open-cast Au-Ag-Pb-Hg-Sb occurrence/mine located in sec. 6, T11N, R4W, and in sec. 1, T11N, R5W, MDM, 2.4 km (7,900 feet) WNW of the Knoxville Mine. Discovered 1865. Worked 1863 - 1877, 1892 - 1905, 1916, 1927, 1932 - 1933, and 1936 - 1945. Some operations extended into Yolo and Lake counties.

The McLaughlin deposit is a large hot spring-type gold deposit located in the northern Coast Ranges of California at the faulted lithologic contact between the Coast Range ophiolite and the Great Valley sequence. The McLaughlin deposit is centered around the sheeted vein complex, a large multistage vein swarm, localized in a dilation zone formed by rheologic contrasts in the footwall polymictic melange. The surface expression of the sheeted vein complex is a subaerial sinter terrace, which merges into the sheeted vein complex. Metal zoning in the sheeted vein complex is highly telescoped. The sinter is enriched in mercury, whereas gold and silver are restricted to the upper 350 m. with the proportion of gold to silver decreasing with depth. Gold is typically present as electrum and is associated with silver and base metal-bearing sulfosalts. Below 350 m mineralization is dominated by small quartz veins with base metal sulfides.

Mineralization is a hydrothermal vein deposit. Host rock is aphanitic volcanic rock (tuff). The ore zone is irregular at 1609.3 meters (1 mile) long and 30.48 meters (several hundred yards ?) wide. The ore occurs as irregular veins of cinnabar filling joint cracks in Tertiary olivine basalt and is disseminated in the rocks adjoining the veins. Alteration is local: silicification of fault zones and tuff; bleaching and kaolinization of basalt. Volcanics are overlain by hot springs deposits.

Production: Ore ran more than 32-50 pounds/ton hand cobbed. Assay given as 18,520 grams/metric ton.

Prior to mining, the total resource of the deposit was calculated at 3.5 million ounces of Au contained within 24.3 million tonnes of ore.
The Pleistocene (<2.2 Ma) McLaughlin low-sulfidation epithermal deposit is located along the moderately northeast dipping Stoney Creek fault, which separates serpentinized ultramafic and mafic rocks of the Middle Jurassic Coast Range ophiolite in the southwest from hangingwall mudstone of the Late Jurassic to Early Cretaceous Great Valley sequence to the northeast. The main ore body comprised a pipe-like sheeted vein complex formed in a dilatant zone between basalts and a mélange of sedimentary rocks and serpentinite. The sheeted vein complex is up to 100 m in width and is composed of centimeter to meters wide, crosscutting opaline veins. The opaline veins locally contain large gold dendrites hosted by fine-grained silica (Fig. 3b). The sheeted vein zone is capped by a siliceous sinter terrace containing interbedded hydrothermal eruption breccia.

Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.

Mineral List

28 valid minerals.

Rock Types Recorded