Geochemical Studies Summary

Geochemical

Geochemical TITLE: Baseline Geochemical Characterization RELEASE DATE: June 2007 PREPARED BY: Tetra Tech Brief Summary: Management of materials is vital to the success of operations planning. As part of the feasibility-level design work, Tetra Tech characterized the tailings and waste rock materials, with the goal of defining the material that will be placed in the waste rock storage area. The initial sample selection consisted of 375 coarse reject samples collected from geologic core drilling series that were cored and logged by Rosemont Copper. Characterization is defined as the geochemical makeup and their potential affect on the environment of the materials being handled and processed at the site.

In general, the results from Synthetic Precipitation Leaching Procedure testing were below the detection limits for most metals based on the analytical method used. The results of the Meteoric Water Mobility Procedure testing also showed that most elements were below the method detection limit. Other tests conducted on the samples included acid-based accounting, kinetic, and whole rock analysis. The tests indicated that the waste rock is not acid generating and will not cause or contribute to a violation of water quality standards.

Geochemical studies looked at the amount and type of materials that may be produced by the Rosemont project, and potential impact on groundwater and surrounding soils.

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TITLE: Bolsa Quartzite – Acid-Base Accounting Properties and Humidity Cell Testing Results RELEASE DATE: October 2009 PREPARED BY: Tetra Tech Brief Summary: The geochemical testing program characterized the acid-base accounting properties of the expected waste rock materials. Portions of the Bolsa Quartzite have the potential, upon weathering, to generate low-pH leachate. The Bolsa Quartzite is anticipated to comprise only 1.9 percent of the total waste rock mass, and 11 percent of the final pit exposure wall. Therefore it will be easy to blend with other acidneutralizing rock types. In the expected pit lake, any acidity generated by the Bolsa exposed in the pit wall will be neutralized by the pit lake water and buffered by the predominantly acid-neutralizing rock types.

TITLE: Geochemistry Characterization Addendum 1 RELEASE DATE: November 2007 PREPARED BY: Tetra Tech Brief Summary: This addendum to Tetra Tech’s Baseline Geochemical Characterization Report focuses on potential water quality impacts in the waste rock storage area and the dry stack tailing facility. Much of the material is considered inert and requires no additional characterization. Some additional characterization and additional sampling may be required as part of the final design phase of the project.

TITLE: Evaluation of Rosemont Geochemical Testing Results and Local Water Quality RELEASE DATE: May 2009 PREPARED BY: Tetra Tech Brief Summary: The Rosemont Copper project includes a Heap Leach Facility, a Waste Rock Storage Area, and a Dry Stack Tailings Facility. This Technical Memorandum from Tetra Tech presents: 1) a summary of the acid-base accounting (ABA) properties of the waste rock and tailings samples tested to date, and 2) an evaluation of geochemical leaching results from waste rock and tailings relative to both local ground/surface water conditions and to Arizona standards for human drinking water and agricultural livestock watering.

Evaluation of ABA data for the Rosemont geologic materials tested to date indicate that the bulk waste rock and tailings properties are classified as inert and are non-acid generating. Evaluation of short-term leach test data from waste rock and tailings showed that bulk leachate composition, as measured by total dissolved solids (TDS), was within the range of natural TDS values observed in stormwater and groundwater. Arsenic concentrations, while exceeding the human drinking water standard, approximate naturally occurring levels, they are within livestock ranges and indicative of the rock type rather than a change in chemistry due to operational processes. It is unlikely that seepage from the Rosemont facilities will significantly change the chemical compositions of the groundwater at the site.

TITLE: Rosemont Geochemical Sample Composite Method RELEASE DATE: November 2009 PREPARED BY: Tetra Tech Brief Summary: Tetra Tech used composites of waste rock samples to test for geochemical characterization.

More than 200 composite samples of drill core and other coarse rejects, representing waste rock material,

were tested in conjunction with the Phase 1 and Phase 2 geochemical testing programs.

The coarse reject material was bagged in five foot intervals. The intervals selected for testing totaled approximately 50 feet of continuous drill core for a particular rock type. Once all coarse reject bags were collected, the bags were shipped under chain of custody for compositing.

The materials were combined and run through the splitter until a well-homogenized sample was achieved.

The material was then reduced to the appropriate testing volume.

TITLE: Geochemistry Sample Update RELEASE DATE: November 2009 PREPARED BY: Tetra Tech Brief Summary: A Tetra Tech review of the 20062007 geochemical testing data was conducted for the Rosemont project to identify potential data gaps in the waste rock characterization program. A statistical evaluation of the acid-base accounting (ABA) data indicated that additional characterization was needed to ensure that all rock types were adequately characterized with respect to their acid-generating capacity.

Upon completion of the 2006-2007 geochemical testing, a total of 165 rock samples were tested for ABA. In 2008, an additional 43 rock samples underwent ABA testing, bringing the total to count to 208 samples.

The majority of samples are classified as non-acid generating. Four samples of the Bolsa Quartzite tested in 2008, were considered potentially acid generating.

These results suggest additional characterization should be conducted on this rock type using humidity cell testing.

TITLE: RCC Geochemical Pit Lake Predictive Model RELEASE DATE: February 2010 PREPARED BY: Tetra Tech Brief Summary: Tetra Tech used Montgomery & Associates pit filling data as an input to a geochemical pit lake predictive model. The model showed the quality of the pit lake water was only slightly changed from local groundwater after 200 years of simulation. The data shows that development of an acidic pit lake is not expected, even beyond the 200-year modeling period.

Laboratory testing was conducted to determine the chemical loading terms required for the geochemical model. All of the parameters modeled were below the primary Aquifer Water Quality Standards (AWQS) for drinking water in Arizona at the end of the 200-year simulation period.

TITLE: Rosemont Geochemical Pit Lake Predictive Model Summary RELEASE DATE: August 2010 PREPARED BY: Tetra Tech Brief Summary: Once mining and mineral processing activities cease, dewatering of the open pit will be terminated. Montgomery & Associates’ 2009 groundwater flow model for the Rosemont site concluded that a pit lake is expected to form in the open pit; and based on the expected inflows to the pit lake in relation to the annual evaporation from the pit lake surface, the pit lake will be a hydraulic sink. The overall effect of the hydraulic sink will be to draw water into the system and not allow water or its associated chemical mass to exit the pit (M&A, 2009).

In addition to the hydrogeological analysis performed by M&A, the expected chemical conditions within the pit lake were analyzed by Tetra Tech. The quality of the pit lake water was only slightly changed from local groundwater after 200 years of model simulation. The development of an acidic pit lake is not expected, even beyond the 200-year modeling period.

TITLE: Geochemical Pit Lake Predictive Model Revision 1 RELEASE DATE: November 2010 PREPARED BY: Tetra Tech Brief Summary: Tetra Tech analyzed the chemical conditions within the anticipated pit lake at Rosemont, including geochemical testing of the materials comprising the ultimate pit walls and the quality of local groundwater. Most of the water reporting to the pit lake will come from local groundwater, with the remaining comprised of direct precipitation and runoff from the pit walls. The pit lake model showed that the quality of the pit lake water was only slightly changed from local groundwater after 200 years of simulation.

At the 200-year simulation mark under the elevated chemical loading scenario, the concentrations of some dissolved chemical constituents were shown to increase by a factor of up to 1.7 relative to local groundwater due to the evaporative loss of water.

Even in the elevated chemical loading scenario, metals are expected to remain at levels in the parts per billion range (less than one part per million).

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TITLE: Site Surface Soils Geochemistry RELEASE DATE: January 2010 PREPARED BY: Tetra Tech Brief Summary: Technical Summary: This technical memorandum from Tetra Tech assessed the potential for leaching of pollutants from surface soils via seepage generated from the dry stack tailings facility or waste rock storage areas.

Soils located in the vicinity of the proposed open pit have the potential to release higher concentrations of certain constituents (e.g., arsenic, iron, and sulfate), when compared to soil from the proposed dry stack tailings facility and waste rock storage area. This is due to the natural mineralization present in the pit area. Under actual field conditions, the leachate will be subject to additional natural dilution, dispersion, and attenuation processes, and it is unlikely that seepage from the Rosemont tailings or waste rock facilities will cause additional significant release of pollutants from project site soils.

TITLE: Tailings Geochemistry RELEASE DATE: October 2008 and March 2009 PREPARED BY: Tetra Tech Brief Summary: Tetra Tech tested four samples of tailings materials for acid-generating capacity and metal release using standard static and short-term leaching procedures. Results indicate that the tailings material generally contains less than 0.01 percent sulfide-sulfur, can be classified as inert with respect to acid generation, and posses a high capacity for acid neutralization.

TITLE: Rosemont Tailings Geochemistry Sample Sources Update RELEASE DATE: August 2010 PREPARED BY: Tetra Tech Brief Summary: In addition to the tailings samples prepared in 2006-2008, Tetra Tech prepared six new samples to better characterize the dry stack tailings associated with the proposed Rosemont Copper project. Tailings samples were generated from each of the five major sulfide ore rock units and one composite sample was generated from ore material representing production years four through seven.

Geochemical characterization of the Rosemont tailings samples indicates that the tailings generally contain less than 0.30 percent sulfide-sulfur, present essentially no risk associated with acid generation, and possess a high capacity for acid neutralization. The tailings were also subjected to short-term leaching tests (SPLP and MWMP) which produced only very low 20

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metal concentrations in the resulting leachates.

TITLE: Preliminary Trip Report and Phase 1 Sampling & Analysis Plan RELEASE DATE: July 2006 PREPARED BY: Vector Arizona Brief Summary: Vector staff traveled to the Rosemont site to evaluate the site characteristics including topography, surface water features, and geology. The team also obtained geologic information to be used in the Phase 1 geochemical sampling program. Phase 1 included visiting the site to assess and take samples.

In Phase II, Vector collected and analyzed samples for static geochemical tests.

TITLE: Waste Rock Material Characterization RELEASE DATE: January 2010 PREPARED BY: Tetra Tech Brief Summary: Tetra Tech prepared an estimate of the waste rock material composition within the Rosemont Ridge Landform based on a mine production schedule provided by Rosemont Copper. The estimate was based on timing of material excavation and development of the facilities as defined by the schedule.

A soil layer may be placed on the outer surfaces and tilled/ripped into the waste rock. The soil layer may include salvaged soil and tertiary gravel from within the limits of the open pit or the Rosemont Ridge Landform.