Craig Keith Miller

The Mindamar Mine exploited a group of lenticular bodies of sulphides that occurred within a persistent, wide, and steep shear zone. The mineralization consists of extremely fine-grained pyrite and sphalerite with minor amounts of chalcopyrite, galena and tennantite. The host rocks for the deposit have been correlated, on lithologic similarities, to the Bourinot Group of Middle Cambrian age.

The genesis of the deposit, as well as the relative ages of the host rocks and mineralization, have been a matter of controversy. This study was undertaken to clarify the geologic setting, geologic history, and environment of base metal deposition at the Mindamar Mine.

The geometry of the rock-types at the mine was interpreted from diamond drill core found abandoned on the mine property. Descriptive drill logs of a previous program, and mine plans of the early workings were re-interpreted and their data was incorporated into a new interpretation for the deposit, using a new nomenclature for the rock-types. This nomenclature was established from specimens collected from the drill core, outcrops and from the mine dumps.

The bulk of the ore occurred within a northeast-striking, west-ward facing, steeply dipping rock sequence which consists of felsic to mafic lava flows, pyroclastic rocks and related volcaniclastic and chemical sedimentary rocks all of which were intruded by mafic sills and dykes. The ore-zone, comprised of a quartz-carbonate rock, massive sulphides, and siliceous siltstones, is stratigraphically controlled, occurring between two chemically distinct volcanic piles, with felsic flows predominating in the footwall, and intermediate tuffs in the hangingwall. The most important concentrations of sulphides occur stratigraphically above the quartz-carbonate within the siltstones. Graded beds and sedimentary layering are present in both the massive banded sulphides and the siltstones.

Superimposed shearing and carbonatization (calcite) processes have modified the primary textures in all lithologies, including the ore and the intrusions which transect it. The introduction of calcite into sheared rocks of all lithologies is not related to the processes that formed the quartz-carbonate rock of the ore-zone.

The ore-zone at the Mindamar Mine was deposited subaqueously as a result of volcanic-related hydrothermal processes, rather than by a younger replacement mechanism. The deposit is interpreted to be a distal-type of the volcanic-exhalative-sedimentary model, analogous to the geologic situation responsible for some of the Kuroko deposits in Japan.

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Pages: 237
Supervisor:  Marcos Zentilli