Abstract

The Mount Morgan mine was closed in July 1981, having yielded 237,896 kg of gold (7,648,533 oz) and 360,616 metric tons of copper from 50 million metric tons of ore, an average recovered grade of 4.75 g/metric ton Au and 0.72 percent Cu. It has been Australia's largest single lode gold orebody and is the fourth largest gold-producing area after the Kalgoorlie Golden Mile and the Bendigo and Ballarat areas (Woodall, 1979).The mine comprises the Main Pipe orebody of pyritic massive sulfides and the adjacent Sugarloaf orebody of siliceous stringer mineralization. When the host stratigraphy is reoriented with respect to regional dip and local faulting, the two orebodies are shown to form a pipelike volcanogenic massive sulfide configuration at a high angle to the stratigraphy.Minor stratiform pyritic mineralization adjacent to the stratigraphic top of the orebody grades downdip away from the orebody to a sequence of interbedded crystal tuffs and cherty rocks with some jasperoid beds.The associated alteration halo of the massive sulfide orebody has been intruded by the Late Devonian Mount Morgan Tonalite. The ore and alteration have been subjected to metamorphism and overprinted by later alteration and additional mineralizing phases, mostly related to the complex tonalite intrusion.The immediate host stratigraphy shows gross thickening and change of character on either side of the orebody, suggesting that the orebody formed along a penecontemporaneous fault. The fault appears to be part of a major resurgent cauldron structure.

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