Mining Intelligence and News
United States

Strong and Harris Project

Click for more information

Categories

Overview

Mine TypeOpen Pit
StagePreliminary Economic Assessment
Commodities
  • Copper
  • Zinc
  • Silver
Mining Method
  • Truck & Shovel / Loader
Mine Life... Lock
SnapshotMining of the Strong and Harris deposit would be by traditional open pit with high-grade underground mining of the remaining sulfides at the bottom of the pit. Processing assumes leaching of oxide and lower-grade mixed material in a single leach pad located to the west of the ultimate pit. In addition, higher-grade mixed material and sulfide material are planned to be processed using flotation and concentration of material.

2024 Guidance: PEA update / Resource Exploration.

Owners

SourceSource
CompanyInterestOwnership
Excelsior Mining Corp. 100 % Indirect
The Strong and Harris project is held by Excelsior through its wholly owned subsidiaries Excelsior Mining Arizona, Inc. and Excelsior Mining Holdings, Inc.

A total of 77 unpatented mining claims are held by Excelsior Holdings that cover 1,296 acres, and 36 unpatented mining claims are held by Excelsior Arizona that cover 612 acres.

Contractors

Lock

- subscription is required.

Deposit type

  • Skarn
  • Porphyry

Summary:

The Strong and Harris copper-zinc-silver deposit is a sub-type of or related to a classic copper skarn (Einaudi and Burt, 1982; and Meinert et al, 2005). Skarn deposits range in size from a few million to 500 million tonnes and are globally significant, particularly in the southwestern US. They can be stand-alone copper skarns, which are generally small, or can be spatially and temporally closely associated with porphyry copper deposits, in which case they tend to be very large. The skarn at Strong and Harris and collectively in the Cochise mining district is presumably related to the Texas Canyon Quartz Monzonite, despite the intrusive itself hosting very little known economic mineralization. Mineralization in the quartz monzonite would require more specialized conditions involving the metal and volatile content of the magma, depth of emplacement, or other factors (Burt, 1977).

Copper skarns generally form in calcareous shales, dolomites and limestones peripheral or adjacent to the margins of diorite to granite intrusions that range from dikes and sills, to large stocks or phases of batholithic intrusions, and frequently are associated with mineralized intrusions. Copper mineralizing hydrothermal fluids are focused along structurally complex and fractured rocks and convert the calcareous shales and limestones to andradite-rich garnet assemblages near the intrusive body, and to pyroxene and wollastonite rich assemblages at areas more distal to the intrusive. Retrograde evolution of the hydrothermal fluids produces actinolite-tremolite-talc-quartz-epidote-chlorite assemblages that overprint earlier garnet and pyroxene. Strong and Harris occurs approximately two miles north of any known occurrences of the Texas Canyon Quartz Monzonite intrusion in the Cochise mining district, which is thought to be the source of mineralizing hydrothermal fluids. Therefore, Strong and Harris can be subcategorized as distal skarn related to a porphyry copper system. This assumption is supported by the high abundance of wollastonite alteration in the mineralized zones. The anatomy of a telescoped porphyry copper system model by Sillitoe (2010) can be used as a conceptual model to understand the spatial relationship of the Strong and Harris distal skarn and associated proximal skarns in the district.

Primary copper-zinc-silver mineralization at Strong and Harris is characterized by lenses of sulfide minerals emplaced more-or-less parallel to layering in favorable lithologic units, usually along bedding planes or in disseminated masses and blebs. Some mineralization is disseminated in certain lithologies. Less frequently, the mineralization is hosted in quartz +/- calcite +/- feldspar veins. The mineralization is typically accompanied by calc-silicate alteration of the carbonate host-rock (described as “tactite” in the logs). In some local areas or sub-units, the mineralization completely replaced the host rock with massive lenses or patches of sulfide minerals, some of which are now oxidized. The sulfide minerals include pyrite, pyrrhotite, chalcopyrite, chalcocite, and sphalerite. Minor tetrahedrite group minerals have also been reported in the historical drill logs.

Sub-units of the Earp Formation, particularly those immediately below its upper contact with the Colina Limestone, were the most favorable sites for deposition of the copper, zinc and silver minerals. However, mineralization is also present in the Colina Limestone above the Earp, as well as in the Horquilla Limestone below the Earp. Historical reports often referred to mineralization in the Horquilla as the “Peabody Sill”, as such mineralization and its host rock were termed at the historical Peabody Mine southwest of the Strong and Harris deposit. The contact between the Horquilla and this sill at the Peabody Mine was reportedly favorable, at the mine although the sill itself is thin and represents only a volumetrically minor portion of that deposit. The same relationship is observed on the western side of the Strong and Harris property where the diabase sill has been logged in several holes and is often mineralized. The thickness of the sill is typically less than 10 feet. Mineralization in tactites of the Horquilla Limestone, either stratigraphically above or below the sill, is equally if not more important than the sill itself at Strong and Harris. However, the sill is a favorable host where present.

The Strong and Harris deposit has been oxidized to varying degrees that generally decrease with depth. Three oxidation zones are currently recognized in the deposit: the oxide zone, the transition (or mixed) zone, and the sulfide zone. In the oxide zone, copper is dominantly hosted in chrysocolla with minor azurite, malachite, and tenorite. Zinc minerals noted in the oxide zone include rosasite, aurichalcite, and willemite. Sulfide zone mineralogy is dominated by chalcopyrite and sphalerite with associated pyrite and pyrrhotite. In the transition (mixed zone), the mineralogy consists of secondary sulfides (namely chalcocite) mixed with a combination of the above oxide and sulfide zone mineralogy.

Reserves

Lock

- subscription is required.

Mining Methods

Lock

- subscription is required.

Comminution

Crushers and Mills

Lock

- subscription is required.

Processing

Lock

- subscription is required.

Production

CommodityUnitsAvg. AnnualLOM
Copper M lbs 62437
Zinc M lbs 82575
Copper Equivalent M lbs 648,007

Operational metrics

Metrics
Annual processing rate  ....  Subscribe
Stripping / waste ratio  ....  Subscribe
Waste tonnes, LOM  ....  Subscribe
Ore tonnes mined, LOM  ....  Subscribe
Total tonnes mined, LOM  ....  Subscribe
Tonnes processed, LOM  ....  Subscribe
* According to 2021 study.

Production Costs

CommodityUnitsAverage
Cash costs Copper Equivalent USD  ....  Subscribe
Assumed price Zinc USD  ....  Subscribe
Assumed price Copper USD  ....  Subscribe
* According to 2021 study / presentation.

Operating Costs

Currency2021
OP mining costs ($/t mined) USD 2.27 *  
OP mining costs ($/t milled) USD  ....  Subscribe
Processing costs ($/t milled) USD  ....  Subscribe
G&A ($/t milled) USD  ....  Subscribe
Total operating costs ($/t milled) USD  ....  Subscribe
* According to 2021 study.

Project Costs

MetricsUnitsLOM Total
Initial CapEx $M USD  ......  Subscribe
Sustaining CapEx $M USD  ......  Subscribe
Total CapEx $M USD  ......  Subscribe
OP OpEx $M USD  ......  Subscribe
Processing OpEx $M USD 353.3
G&A costs $M USD 14.4
Total OpEx $M USD  ......  Subscribe
Income Taxes $M USD  ......  Subscribe
Total Taxes $M USD  ......  Subscribe
Royalty payments $M USD  ......  Subscribe
Net revenue (LOM) $M USD  ......  Subscribe
Pre-tax Cash Flow (LOM) $M USD  ......  Subscribe
After-tax Cash Flow (LOM) $M USD  ......  Subscribe
Pre-tax NPV @ 8% $M USD  ......  Subscribe
After-tax NPV @ 5% $M USD  ......  Subscribe
After-tax NPV @ 10% $M USD  ......  Subscribe
After-tax NPV @ 8% $M USD  ......  Subscribe
Pre-tax IRR, %  ......  Subscribe
After-tax IRR, %  ......  Subscribe
After-tax payback period, years  ......  Subscribe

Required Heavy Mobile Equipment

Lock

- subscription is required.

Personnel

Mine Management

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Sep 9, 2021
....................... Subscription required ....................... Subscription required Subscription required Sep 9, 2021
....................... Subscription required ....................... Subscription required Subscription required Jan 2, 2024

Lock

- subscription is required.