From: "Mardee S. Briscoe" <mbriscoe@jaba.com>
Organization: JABA (US) Inc.
IN SITU LEACH - SOLVENT EXTRACTION-ELECTROWINNING -- (ISL--SX-EW) -
CLARIFIED -
August 19, 1998
By: Dr. John Guilbert, Chairman of the Board
So many JABA shareholders have expressed pleasure at our last explanatory statement, but still queried some aspects of the significance of what we have termed "ISL-SX-EW", that we here provide another clarification. The implications of this recently-developed technology are so phenomenal for JABA shareholders that we want all of you to understand our optimism. Please hang in there and read this whole page!
First off, the huge copper deposits of western North and South America called 'porphyry coppers' - like those at Bingham Canyon Utah, Butte Montana, San Manuel, and Morenci Arizona - contain their copper in a family of minerals called 'sulfides', in which copper and sulfur were combined deep in the earth when the ore deposits formed millions of years ago. These sulfides (which do not dissolve in leach solutions), mostly the mineral chalcopyrite (pronounced 'kalko-pie-rite'), are spread evenly or shot through (disseminated in) the ore rock, requiring that the rock from most 'porphyry copper' mines be excavated, taken to a millsite, crushed to powder consistency, and run through a plant that separates the copper-bearing sulfides from the waste minerals. The copper sulfides are then taken to a smelter where they are roasted to drive off the sulfur, leaving copper metal behind. The sulfur is collected and mixed with water to form sulfuric acid which is used for various industrial purposes including leaching oxide copper. This 'conventional mining and extraction' process leaves an open pit and piles of waste material and smelter slag like the ones at Butte, Montana or Bisbee, Arizona. Costs are normally considered high - up to 75 to 90 cents per pound of copper produced.
Many of the 'porphyry copper deposits' were geologically thrust upwards long ago, became exposed to ancient weathering at and beneath the earth's surface, and had their original chalcopyrite sulfides changed to other sulfide minerals that are soluble in weak sulfuric acid - the same acid that results from natural oxidation of sulfides. These ores have generally been mined from open pits, hauled, placed in dumps (large piles with impermeable "plastic lined" bottoms known as pads), and then sprinkled with a weak acid solution in water that dissolves the contained copper. The solvent solution trickles down through the dumps to an impermeable pad, dissolving copper as it goes, and then the copper-laced fluid travels along the pad to collection ponds from which it is piped to a plant for chemical removal of the dissolved copper. This method is called 'heap leaching' and solvent extraction. After the leaching is finished, the piles of copper-stripped rock are left in place near the original mine site. Although the leaching process is relatively inexpen- sive, overall costs are moderate to high because the ore rock has to be stripped of un-mineralized cover soil and rock, blasted, mined, and transported to the dumps. Costs are generally from 20 to 70 cents per pound of recovered copper.
Now - for geologic reasons too complicated to consider here - a few 'porphyry copper deposits', when they were exposed to weathering and erosion, were oxidized to a different type of mineral, the hydrous copper-silica mineral called 'chrysocolla' (pronounced 'kriss-ah-cola') and other green and black copper oxides. This green mineral forms below the ground surface, typically along a web of veinlets and fractures, but also as spots and masses. In oxide form copper can be dissolved in either a weak acid or alkaline solution. If a solvent could be pumped down one set of drill holes (or 'wells'), it would dissolve the copper out of the chrysocolla. The copper-bearing solution could then be directed through cracks in the brittle rock to another set of wells for out-pumping and removal. This is another style of leaching called in situ leaching (ISL), the chemical leaching of copper from rock that remains in place. The copper is then chemically stripped from the pumped recovery solution (solvent extraction or SX) and electrically 'plated out' to form pure copper cathodes - electro winning or EW (generally 99.999% copper called electrolytic or wire grade copper), thus the 'solvent extraction-electro-winning (SX-EW)' part of the process name. The cost-saving (and profit!) implications of ISL-- SX-EW are huge, because:
(a) up front capital costs are minimal,
(b) the ground surface over the ore remains virtually undisturbed,
(c) the costs of actual mining, removal, and processing of the ore are completely avoided,
(d) there is no mineral separation or smelting process involved,
(e) there remain no unsightly piles of waste rock or slag, and
(f) there will be no post mine clean up and remediation with attendant costs required.
The costs of in situ leaching are on the order of 30 to 50 cents per pound of recovered copper.
JABA's new S.E. Arizona (SEAZ) Project deposit is just such a chrysocolla-oxide copper enriched system, and extraction costs are estimated to be in the 35 to 50-cent range with virtually no disruption of the existing surface. The solvent can be any of several basic types, all of which can be handled in environmental safety. 'Cyanide' is not a candidate solvent - it is used only for recovery of gold or silver, not copper. The most-used solvents are weak sulfuric acid (a very common, safe, and inexpensive industrial chemical and the same naturally occurring acid that created the oxide copper deposit in the first place) and ammoniated water (a safe agricultural fertilizer fluid). The weak sulfuric acid choice is favored by JABA at SEAZ because the ore zones are surrounded by a jacket of limestone, a natural rock of calcium carbonate that reacts instantly with weak sulfuric acid to form calcium sulfate, also known as the mineral gypsum- the material used for the wall board in your homes and offices. The process is 'self-sealing', preventing both copper and fluid loss and protecting the environment.
Test work already performed supports JABA's confidence that SEAZ is an
ideal candidate for the in situ leach - solvent extraction-electrowinning process.
Available on our web site - jaba.com - are some
schematic illustrations and photographs showing ISL - SX - EW and the
more costly and complex standard open pit mining.
--
Mardee S. Briscoe
Vice President/Business Mgr.
JABA (US) Inc.
2766 N. Country Club Rd.
Tucson, AZ 85716
(520)327-7440 voice
(520)327-7450 fax
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