American Bonanza Gold Mining Corp - Bonanza
Home Properties Corporate Info News Releases Share Price Financials Analyst Reports Request Info Disclaimer



General Location Title Geology Mining History
Past Work Programs Recently Completed Programs Current Work Program Future Work Program MRDI Scoping Study

  Technical Report on the Copperstone Gold Property by Michael R. Pawlowski dated Jan. 31, 2005
 Geological Report for the Copperstone Gold Property by Mine Development Associates
     dated October 26, 2000

 Copperstone Gold Project Scoping Study by MRDI Canada dated February, 1999

  • Property covers +8 sq. miles (2,200 HA) - 100% owned through leasehold title, subject to 3% royalty at current gold prices.

  • Former open pit producer – approximately 500,000 ounces of gold were produced between 1987 and 1992.  The approximate average grade for this mine was 0.1 ounces per ton of gold.

  • As reviewed by the MDA report (See Important Information), the Preliminary Assessment by MRDI/Golder Associates estimates the resources for the C and D zones using capped grades as: an Indicated Resource containing 892,000 tons grading 0.32 opt Au (285,700 ounces of gold) plus an additional Inferred Resource containing 1.19 million tons grading 0.35 opt Au (423,000 ounces of gold).  This February 1999 Preliminary Assessment by MRDI/Golder Associates is a "Preliminary Assessment" as defined by NI-43101.

  • As reviewed by the MDA report, MRDI's uncapped resource estimate for these same zones is comprised of 2.1 million tons grading 0.58 opt Au, exceeding 1.2 million ounces of contained gold.  The uncapped resource was estimated by MRDI for comparison purposes, providing an estimate of the affects of capping the gold grades.

  • Within the Indicated and Inferred Resources, MRDI estimated "resources available for mining" as a total of 827,000 tons grading 0.56 opt Au (using capped, diluted grades).  All of these resource estimates by MRDI are not mineral reserves, are based on conceptual mine modelling, and have not yet been shown to be economically viable.

  • Recent exploration for bonanza grade targets identified the D Zone, with the central high grade zone described by three holes with apparently continuous gold mineralization: 15’ @ 4.35 opt Au, 25’ @ 1.6 opt Au, 20’ @ 2.74 opt Au.

  • The first intercept has recently been confirmed by underground channel sampling, as previously announced.  Significant multi-ounce channel samples from the new underground workings include 4.5 feet grading 9.1 opt Au, 1.5 feet grading 11.5 opt Au, 6.4 feet grading 4.1 opt Au, 9.5 feet grading 4.1 opt Au, 2.1 feet grading 3.6 opt Au, 2.1 feet grading 3.2 opt Au, and 5.1 feet grading 2.9 opt Au.

  • Currently drilling from underground and surface to advance the project toward pre-feasibility and define additional gold resources and convert resources to reserves.

[Back to top]


The Corporation holds a 100 percent leasehold interest in the Copperstone Project.  The landlord is The Patch Living Trust and the lease is for a 10 year term starting June 12, 1995, renewable by the Corporation for one or more ten-year terms at the Corporation’s option under the same terms and conditions.  The Corporation is obligated to pay for all permitting and state lease bonding, insurance, taxes, and to pay a sliding scale gross royalty.

The Corporation acquired 75 percent of its interest in the Copperstone mining property from Arctic Precious Metals Inc. (“APMI”), a subsidiary of Royal Oak Mines, in 2002, in a transaction which was subject to a lengthy US Bankruptcy Court process.  APMI has assigned its lease on the Copperstone property to the Corporation so as to bring the Corporation’s interest in the Copperstone mining property from 25 percent to 100 percent, subject only to the existing lease and royalty arrangements.  This acquisition was funded by a loan of US$1,100,000 from Trilon Financial Corporation, now called Brascan Financial Corporation (the “Brascan Loan”) which was completely repaid in 2003.

Mine Development Associates (“MDA”) was requested by the Corporation to complete a technical report on the Copperstone Project, La Paz County, Arizona in accordance with National Instrument 43-101, Companion Policy 43-101CP, and Form 43-101F1.  The scope of the MDA report included a review of pertinent technical reports and data in possession of the Corporation relative to the general setting, geology, project history, exploration activities and results, methodology, quality assurance, and interpretations. MDA visited the property, took samples, reviewed published and unpublished reports, and reviewed and modified the exploration plan. Most of the data addressed in the report was presented to MDA by the Corporation and/or was done by previous workers and including the MRDI Report described below which was included in the MDA Report.  MDA believes the data to be reliable, but has not made a rigorous analysis of the procedures or results.

The MDA Report also refers to and includes as an appendix a report by MRDI-Canada (“MRDI”), currently a subsidiary of AMEC plc, which conducted scoping level studies for the Corporation in February 1999.  The MRDI report was completed prior to the enactment of National Instrument 43-101 and was prepared by MRDI Canada, an independent mining engineering consulting firm.  The report was prepared to industry standards and is relevant and reliable today, as it was in 1999. MRDI did not independently verify the sample data.  The MRDI resource estimate is based on a geological model provided by the Corporation and an inverse distance weighting to the power 3 block model (IDW3).  Gold grades were capped at 2.5 opt gold in the C zone and 4.7 opt gold in the D zone.  A 0.00 opt gold block cut-off grade was used for the total resource estimate.  The tonnage factor applied was 10.7 cu.ft/ton.  The assay database supplied to MRDI contains 30,391 assays from 586 exploration and ore outline drill holes completed during the period 1980 to 1998.  A subset of this database containing 71 drill holes with 253 associated assays has been used in this scoping study to develop the geological and resource model of the C and D zones in the Northwest High Grade Zone.  According to MRDI, the Copperstone Gold Project Resource has been classified into Measured, Indicated and Inferred Resources based upon the level of confidence according to the proposed The Toronto Stock Exchange’s guidelines using the drilling grid spacing and continuity of mineralization as determined through the geological and geostatistical review of the data.

Management is of the opinion that these classifications, based on what was then The Toronto Stock Exchange’s guidelines which subsequently became National Instrument 43-101, with some minor modifications, are materially in compliance with National Instrument 43-101.  The mineral resources disclosed are not mineral reserves and have not yet have demonstrated economic and commercial viability.

[Back to top]


The Copperstone property is located in La Paz County, Arizona, United States. The closest communities are Quartzite, located 16 km to the south and Parker, located 40 km to the north. Phoenix is 106 km east of the Copperstone property. The property is accessible from Phoenix on Interstate 10 to Quartzite and Route 95 from Quartzite.  An 8 km unpaved mine road connects the property to Route 95.

[Back to top]


The Copperstone property consists of 284 contiguous un-patented Federal mineral claims comprising 5,680 acres. The land is under the jurisdiction of the United States Bureau of Land Management (BLM). The Patch Living Trust (“PLT”) of Scottsdale, Arizona owns the title to the 284 mineral claims. In June 1995, the Copperstone property was leased from PLT by APMI for a 10 year term and is renewable at the option of the lessee. The annual claim fees payable to the BLM are approximately US$30,000. An annual US$30,000 advance royalty is payable to PLT under the terms of the lease and is subject to a 1 percent production gross royalty so long as the price of gold in US dollars is less than US$350 per ounce (royalty increases to 6 percent as price of gold increases to over US$551 per ounce).

[Back to top]


Copperstone occurs within the “Basin and Range” province of the south-western USA. The regional geology is strongly influenced by Tertiary age detachment faults and younger high angle normal faults. The Copperstone gold deposit is related to the Moon Mountain or Copper Peak detachment fault. Gold mineralization at Copperstone occurs principally within the moderate to low-angle Copperstone Fault which has been interpreted to be a listric fault associated with the underlying Moon Mountain detachment fault. Gold occurs as native flakes within fault breccia, gouge and shear zones related to the faulting. The wall and host rocks are typically Triassic sediments and Jurassic quartz latite volcanics. Gold is commonly associated with hematite, chlorite, quartz, manganese oxide and copper oxide mineralization.

[Back to top]

Mining History

During the period 1987 to 1993, Cyprus Minerals (“Cyprus”) operated a 2,500 ton per day open-pit mine at Copperstone that produced 500,000 ounces of gold from the Copperstone fault. The mine was closed at the economic limit of open-pit mining. Total mine production was 6,000,000 tons at a grade of 0.11 ounces/ton (3.8 g/t) gold. Gold recovery for the life of mine was 89 percent. The strip ratio of the pit was 10:1. Cyprus drilled 496 reverse circulation and 73 core holes for a total of 569 holes. Following the mine closure in 1993, Cyprus reclaimed the tailings pond and removed the Carbon-in-Pulp mill. Office, shop and warehouse facilities remain at the site. Furthermore, the 69 kv power line and substation remains in service, together with the three water wells with a 200 hp pumping capacity.

[Back to top]

Past Work Programs

Santa Fe Pacific leased the Copperstone property for one year beginning in 1993 and drilled 12,500 feet in 17 wide spaced reverse circulation holes to explore for new gold mineralization. One hole (DCU-08) intersected significant mineralization (0.65 ounces per ton of gold over 15 feet) in the footwall of the Copperstone Fault. This hole was not followed-up and the lease was terminated in 1994. APMI drilled 28,330 feet in 33 surface holes on the property between 1995 and 1997. The main objectives of this drilling were to test for deep, down-dip extensions of the Copperstone Fault below the open-pit and the strike extension of the fault to the north of the open-pit. This drilling resulted in the discovery of high grade gold mineralization on-strike to the north of the open-pit (the “D zone”) and down-dip to the north-east (the “C zone”). The Corporation and APMI entered into the Copperstone joint venture agreement in August, 1998. The Corporation subsequently drilled 10,000 feet in 15 core holes to further define the gold mineralization in the C and D zones. This drilling program was subject to quality control and quality assurance procedures established jointly with MRDI Canada. On completion of the drilling program, MRDI was retained to complete an independent scoping study of a new underground mine in the C and D zones. The MRDI study was completed in February, 1999.

[Back to top]

Recently Completed Work Programs

The Corporation has completed an underground decline which now extends from the northern end of the Open Pit over 1,800 feet to the north, intersecting the southern portion of the D-Zone high grade mineralized target. A cross cut has been driven westward, into the footwall, to establish an underground drill station, Drill Bay #1. Underground channel and panel sampling programs have demonstrated good continuity to the high gold grades in the southern portion of the D-Zone. 

A substantial, detailed underground core drilling program is currently underway. This extensive core drilling from underground will locate and define the grade profile of the Copperstone Fault in the D-Zone, will provide reserve-level detailed data, and will assist in the design of future underground working and stopes.

[Back to top]

Current Work Program

The current work programs at Copperstone fall into two main efforts.  First, drilling programs are underway to convert resources into reserves and increase the confidence level of the resources to the measured resource category.  Second, substantial drilling and other exploration programs are underway to expand the resources through the discovery of new gold zones.

The extensive, detailed core drilling program from underground at the D-Zone represents the most advanced portion of the reserve definition drilling program, and is approximately half complete at March, 2004.  The surface drilling program, with first results announced during March 2004, represents a second front to the resource conversion and confirmation programs.  This effort began during early 2004 and will continue for much of the year, with a total of over 30,000 metres of drilling planned.

The first results of the second main work effort at Copperstone, the exploration for new discoveries, were announced during January 2004.  The Footwall exploration target represents a structure semi-parallel to the Copperstone Fault and an entirely new potential mineralized zone.  Early results are very encouraging and these will be followed up with additional drilling.  Additional exploration programs are underway and will be announced as results are obtained.

[Back to top]

Future Work Program

The next stage of evaluation will be comprised of work programs required to complete a bankable feasibility study. This work will be based on reserves and measured resources, and will focus on metallurgical testing of a bulk ore sample, environmental and geo-technical studies and detailed estimates of the capital and operating costs. 

Current programs of underground core drilling, drifting, cross-cutting and sampling will provide detailed assay and geologic data describing the reserves and resources.  Following completion of this work, if the results warrant, the Corporation will be obtaining an updated independent technical report in accordance with Canadian National Policy 43-101, and will make a production decision for Copperstone.

[Back to top]

MRDI Scoping Study

The MRDI scoping study evaluated the underground mine development of only the C and D zones and calculated an Indicated resource containing 892,000 tons grading 0.32 opt gold (285,700 ounces of gold) and an Inferred resource containing 1.19 million tons grading 0.35 opt gold (423,000 ounces of gold).

Within the above mentioned resource MRDI, on a preliminary basis, evaluated the economics of mining mineralized material which is most available to underground workings from a portal site at the North end of the open pit.  MRDI calculated a diluted, recoverable resource included in the mine design plan of 827,400 tons at a cut and capped grade of 0.56 opt gold (459,500 ounces gold). 

To study this diluted, recoverable resource included in the mine design plan, economic mining cut-off grades were based on a gold price of $300 per ounce, a milling recovery of 90 percent and estimates of operating costs were determined for each zone and varied from about 0.25 to 0.30 opt gold.  A planned daily processing rate of 520 tons per day was used.  The resources available for mining are based on the material within a geologic grade envelope of 0.10 opt gold and greater, and having overall diluted grades greater than the calculate cut-off grades.  The resource for each zone has been factored for 95 percent mining recovery and 10 percent mining dilution at a grade of 0.08 opt gold.  Material excluded from the mining plan includes that with diluted grades less than 0.25 opt gold, totaling about 474,000 tons at a grade of 0.183 opt gold, and that in the hanging wall zones which is based on limited drill hole data and totals about 105,000 tons at a grade of 0.998 opt gold.

MRDI designed a 520 ton per day underground mine plan at the scoping level for the C and D zones. The plan is based on selective drift and fill mining from a decline developed from the base of the open-pit. The mill design incorporates crushing and grinding circuits, a gravity concentrator and cyaninde tank leaching with Carbon-in-Pulp gold recovery. A 90 percent gold recovery has been assumed on the basis of Cyprus historical data.

Capital cost was estimated at US$22.54 million, including direct costs of US$14.67 million and indirect costs of US$7.87 million.  The average mine life operating cost is estimated to be US$74.52 per ton of ore processed.  This total includes mining costs of US$39.64 per ton, processing costs of US$25.21 per ton and General and Administrative costs of US$9.67 per ton.  Annual gold production in year one is forecast to be 156,000 ounces and 72,000 ounces in years two to five.  A pre-tax cash flow analysis of the proposed mine development, assuming a gold price of US$300 per ounce, indicates the following estimated project economics:

  • Cumulative Cash Flow                                       US$ 32 million
  • Net Present Value @ 10 percent discount         US$ 18 million
  • Discounted Cash Flow Rate of Return              45.4 percent
  • Capital Payback                                                 1.2 years
  • Cash Cost of Production                                    US$149 per ounce gold

These project economics are most sensitive to changes in mine grade, metallurgical recovery and gold prices.

[Back to top]