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Ministry of Energy Mines and Responsible for Core Review

Bulletin 31: Geology of the Sheep Creek Camp

by W.H. Mathews, 1953

 

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Bulletin 31 describes the geology of the Sheep Creek camp, which has produced almost two-thirds of the lode gold credited to the Nelson Mining Division.  Although the camp is currently non-productive, it ranks as the sixth camp in British Columbia in terms of total lode gold produced to the end of 1951.

The production of the camp has come from quartz veins that to the end of 1951 have yielded a total of 736,000 ounces of gold, 365,000 ounces of silver, 377,000 pounds of lead, and 312,000 pounds of zinc from 1,720,000 tons of ore.  The production recorded year by year for the camp is set forth in Table VI on page 51.  The accumulated gross value of the gold amounts to more than $24,000,000.  Dividends paid from the profits of mines in the camp, mainly in the period 1935 to 1943, have amounted to $5,400,000.

Two main periods are recognizable in the productive history of the camp.  The first began in 1899, reached its peak immediately before World War I, and ended in 1916.  The second began in 1928 when a new vein on a new property, the Reno, was brought into production.  In the next few years conditions became very favourable for mining gold, and the former producers, the Kootenay Belle and the Queen (Sheep Creek Gold Mining Limited), and a new producer, the Gold Belt, were equipped with modern mills.  Production reached its peak in 1937 and was maintained at more than 135,000 tons a year until 1942.  Thereafter production was mainly from the property of Sheep Creek Gold Mines Limited, which was shut down in 1951 after seventeen years of production.  The camp is now inactive except for minor leasing-type operations.  Both main periods ended in times that were unfavourable for gold mining, the mines being closed after ore that had been developed under more favourable conditions had been entirely or almost entirely exhausted.

The output of the camp has come almost entirely from oreshoots in quartz veins cutting folded quartzites that are part of a thick succession of Lower Cambrian and Precambrian (?) sedimentary rocks.   A very small part of the total gold production has been recovered from narrow high-grade veins in limestone.  The sediments are intruded by several stock-like granitic bodies, by an elongate swarm of quartz porphyry sills, and by numerous lamprophyre dykes.  The granitic bodies are believed to be older than the ore and most of the lamprophyres to be younger.  The quartz veins strike northeasterly across the axes of the folded sediments and generally dip steeply.

The Sheep Creek gold camp is within a district that contains numerous mining camps.  Adjoining and nearby areas are important sources of tungsten and of silver, lead, and zinc.  Several camps have contributed lode gold in varying quantities.   Properties in the several camps of the district have yielded up to 120,000 ounces of gold each.  The occurrences of gold in the district are dealt with briefly in Bulletin 20.  Part 1, Lode Gold Deposits, Southeastern British Columbia, by W.H. Mathews, British Columbia Department of Mines, 1944.   Interest in lead-zinc replacement deposits in areas adjoining the Sheep Creek camp has increased greatly since the field work for this bulletin was undertaken.   Similar lead-zinc deposits have not been discovered within the boundaries of the area treated in the present report.

The sedimentary rocks in the Sheep Creek camp had been highly folded prior to the intrusion of the igneous rocks, and two tight northerly trending anticlines with an intervening syncline make up the major structures of the camp.  Faults belonging to four sets cut across the folded structures (1) A group of northeasterly trending, south-easterly dipping, right-hand strike-slip faults with a small normal component of movement contain all the productive veins, (2) a very few northwesterly trending left-hand strike-slip faults, (3) several northerly trending normal faults; and (4) flat faults along which the hangingwalls have been thrust westward with respect to the footwalls.

The veins occupy the northeasterly trending faults and consist of quartz with minor amounts of pyrite and still smaller amounts of pyrrhotite, chalcopyrite, galena, sphalerite, and gold.  The quartz in the veins is probably derived in large part by recrystallization of quartzite walls.   Visible gold is rare.   The ore is almost without exception confined to parts of the fault zones in which one or both walls are made up of quartzite, and the orebodies are, therefore, found where the veins intersect certain stratigraphic units, notably the quartzite units referred to as Upper Nugget and Upper Navada.  The Motherlode member, also quartzitic, is for some unexplained reason almost completely lacking in orebodies.  The Reno formation, predominantly argillaceous, is almost devoid of ore except in the Reno mine, where the rocks have been conspicuously metamorphosed.  In the veins, the ore occurs in shoots; the other parts of the veins are either too thin, or too low in grade, or both, to justify stoping.  In any one vein the profitable oreshoots have been found within a vertical range of not more than 1,600 feet.   This vertical range for successive veins lies within a depth zone that slopes regularly from the northern to the southern end of the camp.  At the northern end it is 5,500 to 7,000 feet above sea level and at the southern end of the camp, 4 miles distant, it lies entirely below the 3,000 foot level.   Above this zone the vein fracture may persist, but at least within the quartzites, the veins are too narrow to contain orebodies.   At the bottom of the zone, the veins persist and may be even wider than within the zone.  A few veins have been explored at depths of not more than 250 feet below the bottoms of the deepest stopes.  Although these veins are of good width, the parts rich enough in gold to constitute oreshoots were too small and too widely scattered to encourage further exploration and development.  Within the favourable wallrocks and within the favourable depth zone, those parts of the veins striking most nearly east are more likely to contain ore.

Displacement on vein fractures is variable, and in any one vein, other things being equal, the width increases with the amount of displacement.  However, the vein filling is not necessarily wide in vein fractures on which displacement has been large, nor narrow in those on which displacement has been small.

The grade of vein matter is exceedingly variable, patches of high-grade ore being distributed apparently at random within a vein.   The area of such a patch measured in the plane of the vein is rarely more than a few hundred square feet and commonly is much less.  In general patches of ore of which the grade exceeds 5 ounces of gold per ton are larger and more common in the upper part of the productive zone than at greater depths.

 

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