Sandman Project, Ten Mile Mining District, Humboldt County, Nevada, USAi

Regional Level Types
Sandman Project	Project
Ten Mile Mining District	Mining District
Humboldt County	County
Nevada	State
USA	Country

Structure: Bedding plane faults and fractures that crosscut bedding,

Alteration: Silicification

Commodity: Ore Materials: gold, electrum, petzite, possibly sulfides Gangue Materials: quartz, adularia, possibly sulfides

Deposit: Mineralization occurs in Tertiary tuffaceous and volcaniclastic rocks. Mineralization is comprised of stockworks and veins which are typically open spaced and vuggy grading into wider silicified zones at depth. High-grade gold pockets (typically greater than 30 g/t Au (1 opt Au) were located with a metal detector and appear to be localized along a fault surface. Most of the gold is found along the footwall, where open space filling occurred during gold deposition; gold was concentrated in areas where solutions pooled. The presence of some microbreccia and pebble breccia fragments suggest that the fault was reactivated post-mineralization. Occasionally euhedral gold leaves are found rolled up with and within small breccia fragments, also indicating post gold movement. Mineralization appears to follow bedding plane faults and fractures that crosscut bedding, the largest observed gold-bearing vein strikes N. 55-60E and dips to the 55-65 NW. A second location where gold was found in situ is at the intersection of N-S and NE-SW trending structures that converge and can be traced to the surface. Evidence exists of supergene enrichment in the upper zones where some exceptionally rich pockets of gold were found concentrated in favorable structural traps. Thus, crystalline native gold is believed to be bi-modal in origin. Primary gold is represented by electrum (600-650 gold fineness) and minor petzite associated with partially oxidized pyrite and secondary alteration products in a gangue of quartz and adularia. The electrum forms crystalline leaves, reticulated dendrites, and rough grains. The second form, believed to be supergene has a much higher fineness and often forms small platelets, wires, and euhedral crystals derived from altered protore and concentrated by residual and supergene processes in the oxidized levels of the mines. The structurally controlled small, bonanza style gold deposits are hosted in Tertiary tuffaceous and volcaniclastic rocks, mostly under pediment gravels and sand.

Deposit type: Low-sulfide Au-quartz vein

Development: The Ten Mile district was reportedly active from about the early 1900s to the 1940s, with some production judging from the size of the dumps of the old underground workings. No significant production has occurred since then, although several claims are active in the area and in recent years prospectors with metal detectors have reported substantial finds of nuggets and pocket gold around the district.

Ore(s): Gold is localized along fault surfaces and intersections. Most of the gold is found along the footwall, where open-space-filling occurred during gold deposition; gold was concentrated in areas where solutions pooled. The presence of some microbreccia and pebble-breccia fragments suggest that the fault was reactivated post-mineralization. Mineralization appears to follow bedding plane faults and fractures that crosscut bedding.

References

Other Databases

Link to USGS MRDS:	10310414