Objective

Provide the U.S. mining industry with technology for designing environmentally sound, low- cost in situ leach mining operations to produce copper from small, deep, and/or low-grade copper oxide deposits.

Approach

Investigate the feasibility of a new mining method-in situ leach mining-as an alternative to conventional mining for copper. Study fundamental leaching technology that will facilitate future commercial operations. Develop guidelines and procedures that will enable mine operators to design and evaluate in situ leach mining operations for any specific copper oxide deposit.

About In Situ Leach Mining for Copper

In situ leach mining involves the recovery of mineral values from undisturbed ore by circulating solvents, such as dilute sulfuric acid for copper oxide recovery, through the ore in its natural state. In contrast, conventional mining requires mine workers to break the ore and transport it to a processing facility.

An in situ copper mining operation combines surfaceand subsurface facilities in the following manner:

1. Chemicals used to dissolve and maintain the copper in solution are prepared in the surface facility.
2. The solvent is pumped down a set of injection wells and forced into pores and fractures in the rock by using a pressure exceeding the hydrostatic pressure in the deposit.
   
3. As the solvent travels through these flow channels in the rock, it dissolves copper minerals and transports the copper to adjacent production wells.
4. The copper-enriched solutions are collected in the production wells and then pumped to the surface.
5. Copper is recovered from the enriched solutions in a solvent extraction-electrowinning plant; the acid is regenerated in the plant for recirculation through the ore zone. The solvent will make many trips through the ore zone before the copper in a given well pattern will be depleted.

Design Procedures

Duringits research on in situ mining technology, the Bureau developed several “tools” that mining companies may use to design operations for copper oxide deposits. A major design tool consisted of a systematic method for assessing the commercial feasibility of in situ copper mining at any selected oxide deposit.

Developed during a contract study, the method features:

• Identification of site-specific parameters that must be quantified.
• Descriptions of laboratory and field tests to measure these parameters.
• A method for selecting the best mining scenario for any specific site.
• A computer model for determining all capital and operating expenses associated with the well field, solvent extraction-electrowinning plant, and environmental permitting activities. The model also allows a company to conduct an economic analysis of the proposed operation.
• A description of the procedures, specifications, designs, costs for environmental permitting in the State of Arizona.

Bureau researchers also developed techniques for evaluating the influence of geological and geochemical characteristics of an ore deposit on the design of an in situ mining operation. The Bureau developed several computer models describing leaching solution flow in certain hydrologic regimes. Hydrologists need such models to design the most efficient well field.

Further details concerning methods for designing in situ leaching operations for copper oxide deposits, as well as sample applications, can be found in the following contract final reports. These reports are sold by the National Technical Information Service (NTIS). Each volume can be ordered separately at the prices noted.

Volume I, Executive Summary; NTIS No. PB89-148217/AS, $15.95 for paper copy, $6.95 for microfiche.
Volume II, Draft Generic In Situ Copper Mine Design Manual;
NTIS No. PB89-148225/AS, $49.95 for paper, $6.95 for microfiche.
Volume III, Lakeshore Field Experiment and Design of Commercial Scale Operation; NTIS No. PB89-153228/AS, $36.95 on paper, $6.95 on microfiche.
Volume IV, Santa Cruz Field Experiment and Design of Commercial Scale Operation; NTIS No. PB89-153290/AS, $36.95 on paper, $6.95 on microfiche.
Volume V, Field Testing at the Santa Cruz Site; NTIS No. PB89-153303/AS, $21.95 for paper copy, $6.95 on microfiche.

To order, write NTIS at 5285 Port Royal Road, Springfield, VA 22161.

A summary of the Bureau’s most recent developments in computer modeling of solution flow and their applications in designing well fields arc contained in the Bureau’s Information Circular (IC) 9216, “In Situ Leaching Mining.