Economic Geology Vol. 83, 1988, pp. 681-693 ECONOMIC GEOLOGY AND THE BULLETIN OF THE SOCIETY OF ECONOMIC GEOLOGISTS VOL. 83 JUNE-JULY, 1988 NO. 4 A Tightly Folded, Gold-Rich, Massive SulfideDeposit: Que River Mine, Tasmania Ross R. LARGE,PETER J. MCGOLDRICK, RON F. BERRY, Department of Geology, University of Tasmania, GPO Box252C, Hobart, Tasmania 7001, Australia AND CHRIS H. YOUNG Aberfoyle Resources Limited, 1stFloor, 123 Camberwell Road,HawthornEast, Victoria 3123, Australia Abstract The Que River deposit in western Tasmania is a high-grade, gold-rich, Cambrian volcan- ogenicsulfidedeposit, comprising two major subvertical ore lenses hosted by andesitic lavas and volcaniclastics of the Mount Read Volcanics. Contrary to previouspublished interpretations, the major orebodies (PQ and P north lenses) are considered to lie at the samestratigraphic level and be folded into a tight asymmetric syncline which has been sheared along its western limb. Massive sulfides are thickened in the hingeof the syncline. Extensive footwall stringer pyrite-galena-sphalerite mineralization within strongly altered andesitic volcaniclastics occurs on both limbs of the fold. A copper-bearing pyrite-rich stringer zoneoccurs immediately belowthe thickened central section of the PQ lens in the keel of the foldandis interpreted asmarking the principal focus of ore fluidexhalation. Copper, lead, andzincdistribution within the lenses provides evidence of a stratigraphic younging direction around the fold structure. Gold grades of 5 to 30 ppm are concentrated toward the interpreted stratigraphic top of the folded lens. In the hinge zoneof the major fold, pyrite bands within the ore are folded, with galena remobilized into the axial planeof the folds.The galena defines a banding throughout the mine which is subparallel to the cleavage measured in the adjacent alteration zone. The galena banding varies froma spaced cleavage in the moderately deformed zones to a mylonitic foliation in the sheared western limb of the fold. A conspicuous fuchsite-bearing horizon of alteredcoarse-grained polymict volcaniclastic immediately overlies the major ore lenses, and it is in turn overlain by flow-banded dacite lavas and lavabreccias which lack significant hydrothermal alteration. A Cu-rich, massive sulfide body,the S lens, occurs stratigraphically belowandon the eastern side of the PQ lens.This lower lensconsists of massive pyrite andbanded Pb-Zn sulfide overprinted by stringerCu and stringerPb-Zn. Introduction THE Que River mine is one of four high-grade, gold-bearing,polymetallic volcanogenic massive sulfidedeposits locatedin the Mount Read Volcanic arc of western Tasmania (Fig. 1, and Large et al., 1987). The deposit was discoveredin an area of dense rain forestin 1974 by drilling a coincident electromagneticand soil geochemicalanomaly (Webster andSkey,1979). The deposit consists of a series of subvertical lenses (Fig. 2). The published resource of the two majorlenses (PQ andP north) is 2.6 million metric tonsof 7.4 percentPb, 12.9 per- cent Zn, 0.4 percent Cu, 204 g/metric ton Ag, and 3.5 g/metric ton Au. Present production is 300,000 metric tons per annum. Initial interpretations of the local geology by Webster and Skey (1979) and Skey and Young (1980) were basedon surface mapping and a pro- gramof some 200 diamond drill holes. Webster and 0361-0128/88/813/681-13 $2.50 6 81