Gunnison Copper Project


Technical Report

Click here for the complete NI 43-101 Technical Report, Prefeasibility Study on the Gunnison Property - January 2014

Project Highlights

  • Positive Prefeasibility Study Demonstrating $1.24 Billion Pre-Tax NPV and 59.7% Pre-Tax IRR
  • Probable Mineral Reserves of 3.61 billion pounds (632 million tons at 0.29% copper) and Measured and Indicated Mineral Resources of 3.91 billion pounds (683 M tons at 0.29%). Mineral resources are inclusive of mineral reserves.



The Gunnison Property, 2,461 hectares in size, is located 65 miles southeast of Tucson Arizona within the copper porphyry belt.  The towns of Benson and Wilcox are located nearby and can provide skilled labour for the Gunnison Project.  The property is ideally located with access to electrical power on the property, previously developed infrastructure, and supported by an abundant water supply.  The Gunnison Property neighbours several other copper mining developments because it is located within the porphyry belt for copper.

Location Map


Positive Prefeasibility Study

The PFS was completed by M3 Engineering & Technology Corporation ("M3") of Tucson, AZ and is effective as of January 13, 2014. For more information please refer to the News Release dated January 17, 2014.

Highlights of the North Star Gunnison Copper Project PFS “Acid Plant” option include:
  • Pre-tax NPV of $1.24 billion (after-tax $0.824 billion) at a 7.5% discount rate (using a copper price of $2.75/lb)
  • Pre-tax IRR of 59.7% (after-tax 44.7%
  • Pre-tax payback period of 1.8 years (after-tax 2.4 years)
  • Initial estimated capital cost (excluding sustaining capital) of $284.84 million
  • Average life-of-mine operating costs of US$0.69 per pound
  • Other costs of $0.13 per pound, including Royalties of $0.029 per pound
  • Annual production rate of 110 million pounds of copper for the first 14 years, then declining for a 20 year mine life, with a total of 1.682 billion pounds of copper produced over the life of the mine


The PFS illustrates very strong project economics in both the "Acid Plant" and "Non-Acid Plant" scenarios, with the Acid Plant option adding an additional US$174.2 million to the project NPV.



Submerged leach tests

A total of 13 submerged leach tests have been completed from the Lower Abrigo rock formation.  Higher acid concentrations generated faster recovery rates while longer leach times generated higher total recoveries. Based on the sequential head assays, and given sufficient time and acid concentration, it can be expected that copper recoveries could reach 105% to 115% of the acid soluble copper content for the Abrigo Formation and 100% for the Martin Formation.

Table 1 - Results from submerged leach tests

Head Grade1 % Column Flow Rate2 (l/h/m2) Acid Content3 (g/l acid) Days Leached4 Estimated Recovery % Adjusted Acid Consumption5
lb/lb Cu
Cu (total) Cu
Martin Formation
1.22 0.83 0.68 1 22 10 179 61 89 10.1
2 22 5 then 15 then to 20 179 70 98 13.0
3 11 5 then 10 179 60 88 10.0
Upper / Middle Abrigo Formation
0.78 0.61 0.78 4 22 15 119 80 102 7.1
5 37 10 119 76 98 5.7
6 22 10 119 74 95 6.0
7 22 5 119 63 80 4.7
8 11 5 then 10 179 68 99 6.5
Lower Abrigo Formation
0.30 0.19 0.62 9 22 15 99 70 112 9.5
10 37 10 76 68 109 6.3
11 22 10 81 66 106 8.6
12 22 5 99 57 92 4.8
13 11 5 99 61 98 6.3


  1. Calculated head grade: Cu (total) = total copper, Cu (AS) = acid soluble copper, SI = solubility index Cu (AS) / Cu (total)
  2. Flow rate: litres per hour of leach solution applied per cross-sectional square metre
  3. Acid Content: acid concentration of the leach solution in grams per litre of free acid
  4. Days leached includes periods of post leach rinsing
  5. Adjusted Acid Consumption: test acid consumption in pounds of acid consumed per pound of copper recovered adjusted by a factor of 0.5 to compensate for overestimation due to the test protocol

The recovery/time curves for each formation.

recovery time curve 1 sm  recovery time curve 2 sm  recovery time curve 3 sm 

2012 Exploration Results

The 2012 exploration program included diamond drilling for metallurgical testing and for structural, geological and resource definition.

Excelsior completed a total of 10,502 feet (3,150 metres) of diamond drilling with intersections including 0.79% copper over 599 feet in drill hole NSD-24 (see news release dated July 31, 2012).  Detailed drill results and the drill hole location map can be viewed below.

Metallurgical testing included six leach box tests on whole HQ core (~63.5mm diameter), representing a range of rock types and varying from low permeability (low fracture intensity) to high permeability (high fracture intensity).  The results averaged approximately 51% total copper extraction, which is in line with the Preliminary Economic Assessment.  See news release dated November 15, 2012 for full details.

detailed drill results sm

2012 Drill Results

2012drilllocationmap sm 
 Drill Hole Location Map

2011 Exploration Results

33,792 feet (10,300 m) of drilling were completed in May 2011 and have resulted in a significantly increased mineral resource estimate at the North Star Deposit. The oxide copper mineral resource has increased to an indicated resource of 3.21 billion pounds of oxide copper (511 M tons at 0.31%) and an inferred resource of 0.88 billion pounds of oxide copper (159 M tons at 0.28%) (Click here for tonnage and grade details). Further information about the resource estimate can be found in the July 19, 2011 news release.

Comprehensive hydrological testing was completed at the North Star Deposit and resulted in hydrological conductivities in the range expected for a fractured deposit which show the deposit is suitable for ISR. Two hydrological tests were completed on holes NSH-01 and NSH-02 and complement previous testing by Magma Copper Corporation in the mid 1990's. The average K value for the two holes is approximately 2.9 ft/d and are entirely consistent with K values from similar ISR projects. Metallurgical test work on 3 samples returned favorable acid consumption values as well as confirming overall copper recoveries of 40%-50%, which is the expected recovery for an ISR project.

Click here to view the metallurgy report

2011 Drill Results
2011 Drill Results

Drill Location
Plan Map

NSD-1 50
Drill Core

NSD-12 46
Drill Core
Hydrology Drill Hole Locations

click to enlarge

click to enlarge

North Star Long Section

North Star Long Section


Exploration History

There has been no direct mining history on the Gunnison Property; however, there has been considerable mining in the surrounding area that began in the 1880’s.  The North Star and South Star deposits were discovered in the 1960’s and since their discovery several companies have done extensive assaying, magnetic and IP surveys, metallurgical testing, hydrological studying, and leach testing.  In 2006, AzTech became involved in the Gunnison Property and since then, significant testing and analyzing has been completed suggesting that there are strong segments of the Gunnison Property worthy of further exploration and mining.

1960: Deposits were initially discovered by Cyprus-Johnson Mining Company and later mined as an open pit operation with acid leach and electro-winning until 1985.

1970: Drilling and metallurgical testing by Superior Oil Company in the northern division of the North Star deposit.

1974: Quintana Minerals Corporation began diamond drilling and completed metallurgical testing in southern part of North Star.

1993: Magma Copper Company drilled 8 holes, carried out additional metallurgical testing, and completed hydrological studies.

1997: Phelps Dodge Mining Company drilled several holes around the outskirts of the property.

Note: Property was dropped by previous operators due to low copper prices at the time



The Gunnison Project's primary asset is the North Star copper deposit.  It is set in a region characterized by fault-bounded mountains and basins filled with gravels from the Tertiary and Quaternary periods.  Over time there have been several deformations that have affected the mineralogy and formations in the region.  The deposit is identified as a classic Copper Skarn deposit that is considered to be a large size.

The host rock is characterized by mineralized Paleozoic material below a layer of un-mineralized alluvium that ranges from 250-600 feet thick.  There are three main sets of faulting identified including the “Northeaster”, “Easter”, and “Northwester”.  The Paleozoic host rock has been intruded by the Texas Canyon quartz monzonite along the western side of the deposit and has altered the host rock to create zones of calc-silicate and hornfels alteration, as well as low grade copper sulfide mineralization. The copper oxide mineralization extends over 9,800 feet in strike length and is over 900 feet thick in places.  The copper sulfide mineralization formed in the proximal skarn facies which is of higher metamorphic grade and within complex structure zones.  Oxidization of the mineralization occurs at a depth of approximately 1600 feet with the majority of the copper oxide mineralization occurring as malachite and/or chrysocolla.  The remainder of the oxide mineralization occurs as replacement patches and disseminations.

391500 section sm      394500 section sm                 surface geology sm
Section 391500 N
E-W section looking North showing copper bearing formations and resource shells 

Section 394500 N
E-W section looking North showing copper bearing formations and resource shells 

 Surface Geology Map
Showing formations and major structures that exist below the alluvium
           long section sm
North-South Section
N-S long section looking East showing copper bearing formations and resource shells




Submerged leach tests

A total of 13 submerged leach tests were commenced in mid-October 2012.  By early February, 5 of the 13 tests had been completed and the results are presented in Table 1 below. The remaining 7 tests are still under active leaching and are expected to conclude within the next 30 to 60 days (March-April 2013).  The 5 tests completed are from the Lower Abrigo rock formation. The remaining 7 tests are from the Martin formation and Upper/Middle Abrigo formations.

Table 1.  Results from submerged leach tests on the Lower Abrigo formation


Head Grade1, %Cu



Flow rate2, lph/m2

Acid content3, gpl acid

Days leached

Recovery, %

Acid Consumption4 lbs/lbs

Cu total

Cu acid soluble


Cu total

Cu acid soluble
























































  1. Calculated head grade
  2. Flow rate in litres per hour per cross-sectional square metre
  3. Acid concentration in grams per litre of free acid
  4. Acid consumption in pounds of acid consumed per pound of copper recovered

The submerged leach tests employ a different test protocol then the previous “Box tests”, primarily because using the “Box test” protocol does not allow for confirmatory or duplicate tests to verify test results. This new test protocol is similar to the standard column leach test with modifications to more closely reflect the conditions during in-situ leaching.

Figure 1 below shows the recovery time curve for the five submerged leach tests.


Two points are evident from the recovery versus time plot.

a) Higher acid concentrations and higher flow rates (columns 9, 10 and 11) give higher recoveries for any given time, with the highest acid concentration (column 9) giving the highest recovery.  Note: Column 9 was still leaching at the time the column was shut down. 

b) Longer leach times (e.g. column 13) give higher recoveries despite low acid concentration and flow rate.

The submerged leach tests are being conducted by independent laboratory SGS Metcon of Tucson, Arizona under the supervision of Dr. Ronald J. Roman of Leach, Inc., Tucson, Arizona. Dr. Roman has reviewed and approved the technical information disclosed above and is an independent consultant who is a Qualified Person as defined by NI 43-101.

Acid consumption tests

In the North Star deposit most of the copper oxide mineralization occurs as thin coatings on natural fracture surfaces or as thin stringers which offer the least resistance to solution flow and are the source of the permeability within the deposit. During in-situ mining the leach solution will preferentially move through the rock along this mineralized fracture network.

The difficulty arises in collecting and preparing samples for metallurgical testing that precisely mimic natural conditions. The drilling process and subsequent sample preparation cause additional man-made breaking and cutting of the samples, significantly increasing the surface area of the sample exposed to acid. This additional surface area contains no copper mineralization, however they do contain an abundance of acid consuming gangue minerals that would not otherwise have been readily exposed to the acid. The result is a “man-made” increase in acid consumption exhibited by the laboratory test compared to the natural environment of the in-situ leach.

To demonstrate this, two 6” core samples from the Martin formation were collected that had natural, copper oxide mineralized, fractures on each end. The samples were sawn in half down long axis to create two approximately identical halves (two pairs of identical samples). One half of the pair had all the man-made surface area coated with an impermeable acid resistant epoxy to prevent the leach solution from reacting with the un-natural surface area, while the natural fracture surface was left uncoated. The other half of the pair was left uncoated (see photograph below) as would occur in most metallurgical tests including the submerged leach tests described above.

 minnr20130214 fig 1 photo

The samples were submerged in a dilute sulfuric acid solution and the amount of copper leached and acid consumed were monitored. This test is continuing, however results to date are given in Table 2 below.

Table 2. Results of comparative acid consumption tests.



Acid Consumption*, lbs/lb Cu

% change in acid consumption

















* Acid consumption in pounds of acid consumed per pound of copper recovered

The test clearly demonstrates that the epoxy coated half of the pair consumed considerably less acid than the uncoated half. Although qualitative, this experiment clearly demonstrates the man-made over estimation of acid consumption during standard metallurgical testing on higher acid consuming rocks.

The acid consumption tests are being conducted by Mountain States R&D International, Inc. of Tucson, Arizona under the supervision of Dr. Ronald J. Roman of Leach, Inc., Tucson, Arizona. Dr. Roman has reviewed and approved the technical information disclosed above and is an independent consultant who is a Qualified Person as defined by NI 43-101.

Excelsior’s exploration work on the Gunnison Property is supervised by Stephen Twyerould, Fellow of AUSIMM, President and CEO of Excelsior and a Qualified Person as defined by NI 43-101. Unless otherwise indicated, Mr. Twyerould has reviewed and is responsible for the technical information contained in this website.