COLU M SH
LO GICAL SUR
British Columbia Geological Survey Geological Fieldwork 1988
THE WINDY CRAGGY COPPER-COBALT-GOLD MASSIVE SULPHIDE DEPOSIT, NORTHWESTERN BRITISH COLUMBIIA (114P) By J.M. Peter University of Toronto
KEYWORDS: Economic geology, Windy Craggy, volcanosedimentary host rocks, massive sulphide, stockwork and stringer mineralization,hydrothermal alteration, copper, cobalt, gold. tionally, it gives a preliminary descriptiorl of the styles of mineralization and alteration and their spatial distribution within the deposit. The author spent a period of four months at Windy Craggy this past field season and. during this time logged approximately 4270 rnetres of drill ccxe and examined much more in less detail. Approximately two weeks wrespent mapping underground. During the 1987 field seasan about two months were spent mapping and. sampling on the Tats claims, which are located in the immediate vicinity of Windy Craggy; one week was also spent surface mapping at Windy Craggy. This project is part of a Ph.D. thesis in progress at the University o!f Toronto.
The Windy Craggy copper-cobalt-gold massivesulphide deposit is located at 59”44’ north latitude and 137”44’ west longitude in the Alsek-Tatshenshini River area of the the St. Elias Mountains in extreme northwestern British Columbia (Figure 2-12-l). The deposit is in extremely rugged and glaciated terrain and crops out on Windy Peak (Plates 2-12-l and 2-12-Z). Access is by charter fixed-wing aircraft or helicopter. The airstrip at Windy Craggyis located 192 kilometres from Whitehorse, 135 kilometres from Haines, or 62 kilometres from the Haines highway. A I3-kilometre mad built on Tats Glacier leads from the airstrip and camp to the portal and underground workings (Plate 2-12-2). The deposit was discovered during a regional reconnaissance program in 1958 by Frobisher Ltd., now Falconbridge Limited, under the direction of J.J.McDougall. Exploration work was conducted by Falconbridge and its predecessor companies until 1981 when it entered into an agreement with Geddes Resources Ltd. In late 1983 Falconbridge conveyed title to the property to Geddes Resources. In early 1987 Geddes Resources commenced development of a 1852-m&e adit extending close to a gold-enriched part of the deposit. This, and drifting alongside and par&l tothe strike of the deposit on its western margin, was completed in the spring of 1988. Exploration work since then (current to September 1988) has consisted of underground drilling with the intention of defining the extent of gold mineralization and outlining reserves of copper and cobalt. As of September 1988, II 277 metres of underground drilling have been completed and a crosscut was being driveninto massive sulphide mineralization to obtain bulk samples for metallurgical testing (Report to Shareholders, September 7, 1988). Grades and tonnages have not yet been calculated as assaysand geological continuity between sections are still being developed, and only 420 tnetres of strike length has been systematically drilled. Previous estimates of grade and tonnage have ranged from 90 milliontonnes grading 2.8 per cent copper to 320 million tonnes grading 1.52 per cent copper and 0.08 per cent cobalt (for example, Northern Miner, January 13, 1983; Canadian Mining Journal, 1986). This report describes the Windy Craggy deposit and presen& new information on the geological setting obtained from detailed underground drilling, mapping and sampling. AddiBritish Columbia
GEOLOGICAL SETTINGThe Windy Craggy area is situated within the allocthonws Alexander terrane of the Insular tectonic belt (Figure 2- 12-2). Geological mapping by Campbell and Dodds (1979, 1983), Maclntyre (1983, 1984) and Prince (1983) indicates the area is within a broad belt of complexly deformed Faleozoic cl&c and carbonate rocks of relatively low metamorphic grade. The area is underlain by intermediate to...