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NEVADA

The Lost Blue Bucket Mine

GEOLOGY OF THE AREA

The immense wilderness known as "Blue Bucket country" encompasses nearly 40,000 square miles of volcanic badlands that extend from the John Day River of east-central Oregon southward to the Black Rock country of Nevada. Its eastern boundary is formed by the Owyhee Mountains of extreme southwestern Idaho while its western boundary coincides with the Lake region of south-central Oregon. The area is incredibly vast and rugged. It is dominated by an extensive terrain of Tertiary volcanic rocks that includes older mid-Tertiary andesite flows and breccias and younger rhyolite lava flows, related hypabyssal rocks, welded and nonwelded silicic ash-flow tuffs, and abundant basalts and andesites. This volcanic province contains a number of major volcanic vents and domes, most of which occur in south-central Oregon. Faulting is prevalent throughout most of "Blue Bucket country". Most of the faults in southeastern Oregon trend northwest-southeast. A second, less abundant set trends roughly north-south while the least abundant set has a northeast-southwest trend. Most of the northwest-southeast trending faults occur in clusters or swarms that cut across the southeastern quarter of the state. The same fault trends occur in northwestern Nevada and are probably a product of Basin and Range faulting.

The northwestern portion of Nevada consists of a series of north-south trending mountain ranges bounded by deep, alluvium-filled valleys. The mountain ranges are predominantly composed of volcanic lava flows with minor granitic and dioritic intrusions. The Black Rock Range is dominated by a suite of volcanic rocks which include rhyolite lavas and ash-flow tuffs, andesite flows and breccias, and basalts. The Pine Forest Range is geologically more complex. It is comprised of Cretaceous granite with minor diorite, Jurassic to Triassic clastic sedimentary rocks and limestones, older Permian to Triassic andesite flows, breccias, and tuffs, and younger Tertiary andesites. Similarly, the Bilk Creek Mountains are made up of Cretaceous granite with large exposures of Tertiary ash-flow tuffs and andesite and basalt flows. These Cretaceous granites are especially abundant south of Disaster Peak. The Montana and Double H Mountains are almost entirely composed of rhyolitic lava flows and welded ash-flow tuffs.

The southeastern quarter of the state of Oregon is dominated by volcanic rocks of middle to late-Tertiary age. The older volcanics range in age from Eocene to early Miocene and are grouped with several nonmarine clastic sedimentary formations of similar age. The younger volcanics range in age from Miocene to Pliocene and are likewise grouped with clastic sedimentary rocks deposited during the same period. In the southeastern part of the state, these younger Tertiary volcanics consist of basalt and andesite flows and rhyolitic ash-flow tuffs.

The rugged country just east of Lake Abert is home to three small volcanic vents or dome structures. The area is largely underlain by basalts and andesites with several large exposures of nonmarine clastic sedimentary rocks and rhyolitic ash-flow tuffs. Faulting is prevalent in this part of the country, especially along the eastern edge of Warner Valley. Most of the prominent ridges, cliffs, and rims in this part of the country are fault-bounded.

The mountainous country near the northern headwaters of the Malheur and Little Malheur Rivers is mostly underlain by Tertiary basalts and andesites with minor clastic sedimentary rocks. Exposures of older Mesozoic sedimentary and volcanic rocks occur northeast of the confluence of Little Crane Creek and the North Fork of the Malheur River, in the Monument Rock Wilderness area. A number of major northwest-southeast trending faults have been recognized in this region. Most of these coincide with the linear streams and river valleys of southeastern Grant County.

Mineralization is generally weak in the interior of "Blue Bucket country" but moderate to rich along its northern, eastern, and southern margins. Along the southern fringe, the rich mining districts of Varyville, Warm Springs, and Leadville have produced an abundance of precious and base metals. At Varyville, the complex gold, silver, copper, lead, and antimony-bearing ore bodies were emplaced within fault zones in older Mesozoic rocks. In the Warm Springs District, the ore bodies consisted of gold-bearing quartz veins in Mesozoic granite. At Leadville, the silver and lead-bearing veins were found in mid-Tertiary andesites and associated porphyry intrusives.

Along the eastern margin of "Blue Bucket country", the fabulous Silver City District has produced over a million ounces of gold. Here, the rich ore bodies were emplaced within the famous Idaho Batholith.

Along the northern fringe of Oregon's "Blue Bucket country", the state's eastern gold belt has churned out nearly 3 million ounces of gold since its discovery in 1861. The lode deposits in this area consisted of extremely rich gold-bearing veins emplaced within the older country rock.

PROSPECTING POTENTIAL

Prospectors face a daunting task when they enter "Blue Bucket country" in search of the lost mine. The region constitutes one of the most rugged and remote locations in the lower 48. It is incredibly vast and nearly waterless, especially in its southern half. In addition, most of the area is overlain by barren volcanic rocks. Except for the Mormon Basin District and the small Malheur District, the bulk of this extensive volcanic province appears to be devoid of any significant mineral deposits. Only on its northern, eastern, and southern flanks do we see the kind of rich mineral deposits that prospectors dream of. Mineralization seems to be associated with older Mesozoic to mid-Tertiary volcanics and intrusives in these mining districts.

Fault zones can be excellent conduits for mineral-rich fluids. In addition, they provide a locus for mineral emplacement. A number of mining districts along the fringes of "Blue Bucket country" have fault-controlled ore deposits.

Prospectors may want to focus on the areas underlain by older Mesozoic to mid-Tertiary igneous bodies, although in many cases these may be covered by younger basalts and andesites. Prospectors should probably take this into account when searching for the lost canyon of gold. Older mineralized rock could be exposed in some deep canyon in an area otherwise overlain by younger basalt. Prospectors may also want to concentrate on the heavily-faulted areas within these exposures of older igneous rock.

Researchers have placed the Lost Blue Bucket Mine in the Black Rock country of northwestern Nevada, in the Burnt River country of east-central Oregon, in the Lake country of south-central Oregon, and near the northern headwaters of the Malheur and Little Malheur Rivers in east-central Oregon. Prospectors may want to start their search in one of these areas. Metal-detectors may prove to be extremely useful in the search for coarse placer gold along the various canyon floors.