On the Chalcopyrite inclusions in Sphalerite

Abstract

The first purpose of this work was to measure the relative percentages of chalcopyrite inclusions in the well-known intergrowth sphalerite-chalcopyrite, observed in hydrothermal ores. It seems to exist a relation between percentage and hydrothermal intensity, and between percentage and sphalerite variety as well. Low-temperature deposits show percentages of 1-2% of chalcopyrite inclusions in sphalerite, while higher temperature ores show 5-6%. The chalcopyrite inclusions follow: a. sphalerite (110) cleavage planes; b. sphalerite twinning composition surface; c. sphalerite grain boundaries, as blebs or rims; d. subsequent fractures in sphalerite, as veinlets. Etching experiments brought out the texture of the sphalerite, and had small effect upon the chalcopyrite. Aqua regia and nitric acid were the more convenient and satisfactory reagents. X-ray investigation has been carried out mostly by the rotation picture method. The pictures have revealed the orientation of the chalcopyrite inclusions with respect to the sphalerite crystal structure. There is evidence that sphalerite [100] direction is parallel to the chalcopyrite [130] direction, in the specimens studied. Inclusions of dendrite-like sphalerite crystals have been reported in a few specimens of chalcopyrite. Exsolution is the more likely explanation for the chalcopyrite inclusions, inferred from evidences such as: texture of the intergrowth, crystal structure of sphalerite and chalcopyrite, two generations of chalcopyrite, sphalerite inclusions in chalcopyrite, size, orientation, and distribution of the chalcopyrite inclusions