The Los Burros district was organized in 18761, though little but placer mining was done in the region until 1887, when the Last Chance (Buclimo) deposit was discovered by W. D. Cruikshank. Before that time a small quantity of gold was produced yearly by Chinese, who washed the gravels of San Antonio River in the vicinity of Jolon, and a little ragged coarse placer gold had been recovered from the ravines of the Santa Lucia Range near the coast. Cruikshank's discovery at the head of Alder Creek caused only a mild excitement, for the region was rugged, and transportation of supplies and equipment was difficult. In four months after the discovery of the Last Chance sufficient free gold had been saved from the surface workings to pay for the installation of a 3-stamp mill and small boiler on the property. The developments, consisting of open cuts, shafts, and drift tunnels that attained no great depth, showed three nearly parallel quartz veinlets, lying parallel to the bedding of sandstones. A group of claims, including the Mars, Manchester, Grand Pacific, and Ophir, was located near the original discovery, and the Stonewall and Brewery, farther west on Willow Creek, were located during the same year.
Apparently little was done in the district after 1888, except at the Last Chance mine, for the next record of the State mineralogist is for the year 18922 By that time the Last Chance had reached a depth of 160 feet.
Practically all the mining in the district was confined to the mines on Alder Creek until 1902, when the discovery of a few very large gold nuggets on Spruce Creek led to the organization of the Gorda Mining Co., which has done some work to locate the veins that were the source of this coarse gold. About the same time placer gold was found in the gravels of Willow Creek, and very rich quartz float was found on the Plaskett property, called the Ocean View. The Bushnell vein, on the point between Willow Creek and its North Fork, at an elevation of 1,600 feet, was discovered about 1904, and more recently croppings showing copper-stained pyritic sandstone have been prospected in the canyon of the South Fork of Willow Creek, about 2 miles north of the Last Chance mine. The Last Chance and several other properties in the vicinity are now controlled by the Buclimo Mining Co., and the original names have been more or less lost. This company found the upper workings in such state that it began to drive a long crosscut from Alder Creek to tap the veins at a depth of about 400 feet, but this project was not completed.
The total production of the Los Burros district is estimated at $90,0003. The records of the United States Geological Survey show a production of $4,746 in gold and silver for the period 1905-1908, most of it from siliceous gold ores. During another period of activity from 1912 to 1914 a total of 329 tons of siliceous ore was treated, and the total production of the district, including a small quantity of placer gold, was valued at $14,419. There is no record of production from the district since 1917.
In the winter of 1920-21 a little development work was done on the Bushnell, Gorda, and New York properties and some surface work at the Melville and Hammond prospects, on the south side of Willow Creek.ORE DEPOSITS
The principal mineralization of the district is in the vicinity of the serpentine belts, and the greatest amount is at the head of Alder Creek, near the Buclimo, Grizzly, and New York properties. In this locality relatively narrow quartz stringers, from half an inch to 2 inches in width, that strike N. 70°-85° W. and usually dip 60°-85° N., lie parallel to the major structural features. Calcite and siderite in minor amounts are associated with the quartz in most places. Oxidation is relatively shallow, and in some pits sulphides are found directly at the surface. The oxidized surface ores are largely limonite-stained bodies of crushed sandstone, with more or less quartz, and carry free gold. The sulphide ores, which were visible at only a few places in 1921, consist of sandstone cut by veinlets of quartz and a little calcite, which have been crushed and later mineralized. The sulphides are pyrite, arsenopyrite, and minor amounts 0f chalcopyrite, sphalerite, and occasionally a speck of galena. The sulphides are usually confined to the immediate vicinity of the quartz veinlets, though in a few places finely disseminated pyrite, with much less chalcopyrite, is diffused through the sandstone for several feet from the veinlets. Practically all the gold produced from the lodes in the district has been extracted from relatively small lenses of oxidized ore, which required only amalgamation for treatment. It is doubtful if the sulphide ores are sufficiently rich to stand the cost of transportation and treatment by smelting.
At the New York property, on Ajax Mountain near the summit, two narrow veinlets, about 18 inches apart, constitute the lode. The crushed, contorted rocks between theveinlets carry pyrite and arsenopyrite, with very minor amounts of chalcopyrite and galena. Complete oxidation on this lode has extended to a depth of 50 feet, and mining to that depth has yielded some fairly good free-gold ore. Two tunnels, a few hundred feet in total length, have been driven in the sulphide zone. The sulphides are in very small crystals and appear to have been deposited subsequently to a period of crushing of the original quartz veins. Arsenopyrite predominates over pyrite.
The Grizzly ledge, in the bottom of the Alder Creek valley, between the New York and Buclimo properties, measures 3 to 4 feet between walls. The ledge matter is crushed sandstone, with stringers of oxidized quartz and a little calcite. The incline on the ledge, which dips 75° N., is said to be 80 feet deep but was partly filled with water at the time of visit.
1. Trelan, William, California State Min. Bur. Eighth Ann. Rept., pp. 405-410, 1888.
2. California State Mineralogist First Biennial Rept., for the two years ending Sept. 15, 1892, p. 259. 3. California State Mineralogist Fifteenth Ann. Rept., p. 597, 1916.
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