Bulletin . JL (A) Photomicrograph of a polished section of ore from Cornfield Prospect No. 1,showing graphic intergrowth of chalcocite and bornite. This intergrowth isbelieved from general relations to be of hypogene origin, but there is no wayof proving that such is the case. If of supergene origin it offers .strong evi-dence that in this case the alteration has been from chalcocite to bornite, itbeing noted that the bornite occurs in what appears to be a fracture in thechalcocite. This section is another good bit of testimony that the evidenceafforded by graphic intergrowths as to the origin
Bulletin . JL (A) Photomicrograph of a polished section of ore from Cornfield Prospect No. 1,showing graphic intergrowth of chalcocite and bornite. This intergrowth isbelieved from general relations to be of hypogene origin, but there is no wayof proving that such is the case. If of supergene origin it offers .strong evi-dence that in this case the alteration has been from chalcocite to bornite, itbeing noted that the bornite occurs in what appears to be a fracture in thechalcocite. This section is another good bit of testimony that the evidenceafforded by graphic intergrowths as to the origin of the components is, tosay the least, ambiguous. White = chalcocite. Gray = bornite. Black =^ lines = scratches made in polishing. DETAILED DESCKIPTIOX OF THE VEIXS AXD ORES. 91 of the vein, aud through replacenieut of the wall rock by vein matter. Itis also probable that the openings may have been increased by earth move-ments, faulting, etc., along the fractures in which the veins were
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