The Black Rock Range of northwestern Nevada rises up from the arid wastes of the surrounding Black Rock Desert near the western edge of Nevada's Great Basin. The range extends nearly 40 miles from Black Rock Point northward to the Summit Lake Indian Reservation. It is bounded by the Black Rock Desert on its eastern, southern, and western sides.
The Black Rock Range is part of an extensive volcanic "province" made up mostly of mid-Tertiary silicic tuffs, rhyolites, and andesites and late-Tertiary basalts, andesites, and rhyolites. A small remnant of Permian to Triassic andesite with minor clastic sedimentary rocks occurs in the southernmost part of the range near Black Rock Point. In addition, small exposures of late Mesozoic to early Tertiary granitic intrusives occur along the western edge of the range, near Copper Canyon. The bulk of the Black Rock Range is made up of rhyolitic lava flows and associated shallow intrusives. These comprise the majority of the older, mid-Tertiary volcanics in the area. Most of the younger, late-Tertiary volcanics in the range are more mafic in composition, being predominantly basalts and andesites.
As one travels northward from Black Rock Point, along the western edge of the range, first rhyolites and then basalts are encountered as the abandoned site of Hardin City is approached. North of Hardin City, the basalt flows give way to welded ash-flow tuffs, older andesite flows and breccias, and older-still granites and granodiorites.
Faulting is prevalent along the western edge of the range and in the middle of the range, near its crest. Most of the contact between the older rhyolites and younger basalts in the southern half of the range is fault-bounded. The majority of the faults in the Black Rock Range trend roughly north-south.
Mineralization in this part of Nevada is weak and largely confined to the Leadville District and the Varyville District. The Leadville ores consist of silver, lead, and zinc-bearing veins associated with an Oligocene-age dacite porphyry intrusion. The Varyville ores are much richer. Here, the veins are fault-controlled and consist of gold, silver, copper, and lead ores.
The Black Rock Range presents a considerable challenge for the modern-day prospector. The range is remote, extremely rugged, and virtually waterless. It is largely composed of rhyolites, tuffs, and basalts which have so far proven to be largely barren of mineral deposits. The Black Rock Range has been heavily prospected since James Hardin's return expedition of 1859, but no substantial silver deposits have ever been found. Nevertheless, the fact remains that Hardin and Lambert stumbled across a sizeable placer deposit of silver somewhere in the Black Rock Range in 1849. Both had rich samples of silver to prove it.
In this part of Nevada, mineralization seems to be associated with older, mid-Tertiary volcanics and intrusives. Prospectors may therefore want to concentrate on the western flank of the range, in particular those areas underlain by older, intermediate to felsic igneous rocks. The fault zone that runs along the western edge of the range also merits some attention as do the small Mesozoic intrusions near Copper Canyon.