The ore bodies of the Highland-Surprise Mine are replacements along shear zones in quartzose slate, quartzite, and phyllite of the Prichard Formation of the Belt series (Precambrian). Pyrite, arsenopyrite, pyrrhotite, sphalerite, chalcopyrite, and galena are the chief metallic minerals and were probably deposited in that order. Temperatures of formation were estimated for pyrrhotite-pyrite and sphalerite-pyrrhotite assemblages contained in the steeply dipping vein system. Measurements on 62 pyrrhotites indicate a range in temperature of crystallization between 370 degrees and 492 degrees C. (no correction required for confining pressures <2000 bars below 670 degrees C.), and measurements on 14 sphalerites indicate crystallization temperatures between 375 degrees and 460 degrees C. (uncorrected for confining pressure). No systematic temperature gradients were recognized. Minor elements in 23 pyrrhotite, 8 pyrite, 13 sphalerite, and 2 galena samples were determined. Partition ratios of Ni and Co in pyrrhotite-pyrite and sphalerite-pyrrhotite pairs are erratic. This suggests a dis-equilibrium distribution of these elements between the phases of each mineral pair and/or b) crystallization of the mineral pairs under different physical conditions.

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