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Geology and mineralization in the Lorraine property area : Omineca Mining Division, British Columbia. Koo, J.

Abstract

The Lorraine property area occupies the north eastern part of the Duckling Creek syenite located within the central part of the Hogem batholith in British Columbia. The rocks of the Lorraine property area consist of "metasomatic syenites" or "fenites" formed by the metasomatism of the fractured Hogem diorite. They are believed to have been derived from a hypothetical alkaline magma formed beneath the diorite. The residual magma differentiated from the alkaline magma, produced late dykes and hydrothermal fluid. A K-Ar date, 170±8 m. y.(Lower Jurassic) may correspond to both the minimum age of the fenites and the maximum age of the sulphide mineralization at the Lorraine property. Also, the age may mark the time point dividing the first division and the second division of the Hogem batholith. The characteristic minerals of the successive stages of alteration are 1. biotite, 2. albite, 3. orthoclase, if. quartz, 5. sericite, 6. chlorite, and 7. epidote. The altering fluid contained concentrations of soda, potash, silica, hydrogen sulphide, water, and a minor amount of lime. The primary sulphides are bornite, chalcopyrite, and pyrite. The Lorraine deposit posseses no noticeable gossan, but contains secondary copper minerals such as covellite, chalcocite, azurite and malachite. The deposit is divided in plan into three mineral zones on the basis of the primary sulphide assemblages. The dykes, mafic rocks, and fractures were the main controls of mineralization. The composition of the hydro thermal, fluid changed as sulphur reacted with iron of the host rock to form pyrite. The reduced sulphur ratio appears to have caused deposition of bornite and chalcopyrite. In the mineral zones pyrite was replaced progressively by chalcopyrite and bornite. The best classification for the Lorraine deposit is xenothermal.

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