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Gold/Mining/Energy : Medinah Mining Inc. (MDHM) -- Ignore unavailable to you. Want to Upgrade?

To: Mike Gold who wrote (9715)	3/7/1999 6:20:00 PM
From: J. Nelson	Respond to of 25548

Cool Mike I'll bet ya can't wait ! Breathing harder in wait for the news. (eom)

To: Mike Gold who wrote (9715)	3/8/1999 8:47:00 PM
From: Handshake™	Respond to of 25548

Objectives This project investigates a new method for recovery of gold from arsenopyrite involving pyrolysis followed by either (1) direct cyanide leaching of the pyrrhotite product or (2) roasting the pyrrhotite intermediate and cyanide leaching the calcine. Activities Two gold-bearing refractory gold concentrates, one from the New England mine (NSW) and the other from Harbour Lights (WA), were pyrolysed in an inert atmosphere to produce pyrrhotite. Although all the gold had been exsolved from the matrix, it was still encapsulated in the pyrrhotite host. On cyanide leaching, gold recoveries of around 50% and 30% were achieved for the New England and Harbour Lights concentrates respectively. The process was extended to a two stage reaction, the PYOX process. The concentrate was first pyrolysed in nitrogen at 700° C for 30 minutes, which removed the arsenic as arsenic metal, and half the sulfur from the pyrite. The product was roasted in air and oxygen for various times and temperatures. In air, the reaction required at least eight hours in the temperature range 550-650° C to convert the pyrrhotite to hematite. Leaching of the calcine gave recoveries of between 75-86% for the New England concentrate. In oxygen, the conversion of pyrrhotite to hematite was complete in 2 hours. Gold recovery improved to between 80-97%, with the best recovery achieved at a roasting temperature of 550° C. Recoveries from the Harbour Lights concentrate were in general lower, with a maximum value of 79% after two hours in oxygen. However, a 79% recovery was also achieved after an eight hour roast in air. Studies were also carried out on the solubility of natural monoclinic and hexagonal pyrrhotites in cyanide solution. The monoclinic was much more reactive than the hexagonal form, with the former consuming large quantities of cyanide and oxygen from solution.