The Johnson Camp is held by Gunnison Copper Corp. (GCC) through its wholly owned subsidiaries Gunnison Arizona (former Excelsior Mining Arizona, Inc.) and Gunnison Holdings (former Excelsior Mining Holdings, Inc.).
On July 31, 2023, GCC announced that it had entered into an option agreement with Nuton to further evaluate the use of its Nuton™ copper heap leaching technologies at Johnson Camp. Under the Nuton Option Agreement, GCC remains the operator and Nuton funds GCC’s costs associated with a twostage work program at Johnson Camp.
The Nuton Option Agreement required that if Nuton proceeds to Stage 2. After the completion of Stage 2, Nuton will have the right to exercise the option to joint venture and form a joint venture with GCU for Johnson Camp per mutually agreeable terms whereby Nuton would hold an initial 49% and GCC an initial 51%.
- subscription is required.
Summary:
The Johnson Camp Mine is located within the Mexican Highland region of the Basin and Range province, which is characterized by fault-bounded mountain ranges, with large intrusions forming the cores of the ranges. The project lies on the eastern edge of the Little Dragoon Mountains within the Cochise mining district. The Little Dragoon Mountains are an isolated, fault bounded horst block comprised of rocks spanning from 1.4 billion years ago (Ga) Pinal Group schists to Holocene sediments. The southern portion of the Little Dragoon Mountains consists predominately of the Texas Canyon Quartz Monzonite of Tertiary age, whereas the Pinal Group schists and a sequence of Paleozoic sedimentary units dominate the northern half of the range. At Johnson Camp, the important Paleozoic host is the Cambrian Abrigo Formation. The Texas Canyon Quartz Monzonite is porphyritic intrusion that crops out to the southwest of the Burro Pit at the Johnson Camp Mine.
Deposit Type
The Johnson Camp Mine copper deposit is a type of copper skarn. The copper skarn at Johnson Camp and collectively in the Cochise mining district is presumably related to the Texas Canyon Quartz Monzonite. 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 mineralization forms 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 that are subject to retrograde alteration with mineral hydrated silicate assemblages that overprint earlier garnet and pyroxene.
Mineralization
Mineralization at Johnson Camp occurs approximately 500 ft northeast of known occurrences of the Texas Canyon Quartz Monzonite intrusion as proximal skarn related to a porphyry copper system. This assumption is supported by the high abundance of garnet-epidote alteration in the mineralized zones, and the characterization of the deposits in numerous historical publications.
Primary copper mineralization at Johnson Camp is dominantly found along bedding planes or in veins and replacements as chalcopyrite along with quartz and pyrite, closely associated with skarn and calc-silicate alteration in the rock. The presence of copper mineralization at JCM is generally within the Bolsa Quartzite, Diabase Units, Lower and Middle Abrigo Formations. The deposit has been oxidized variably and oxidation is strongly controlled by structural features such as faults and stratigraphic contacts, as well as general depth profiles. Oxide copper consists primarily of chrysocolla, malachite, copper limonite, and manganiferous wad. Supergene chalcocite and occasional native copper occur generally in transitional zones between the oxide and primary sulfide mineralization. Transitional zones void of significant supergene chalcocite are categorized as mixed at JCM. Primary copper mineralization is dominated by chalcopyrite mineralogy. North-northwest and north-northeast fault sets appear to have had some influence on mineralizing fluids although the structural zones themselves are not significant in terms of bulk mineralization. Locally in the diabase sills and Bolsa quartzite, copper has been observed as exotic accumulations on fractures, presumably derived from dissolution of copper in the immediately overlying lower Abrigo Formation. This is especially apparent in the Copper Chief pit, where mobilized and precipitated copper oxides can be easily observed on joint planes and fractures.
Several deformations have occurred in the area with the most recent being the latest Cretaceous-Paleocene Laramide Orogeny compression, followed by Miocene and younger Basin and Range extension that has modified the topography to its current appearance.
The stratigraphy of the Burro pit and Copper Chief pit includes, from lowest to highest, Pioneer shale, diabase sill, Bolsa quartzite, three members of the Abrigo formation, and the Martin dolomite. Most mineralization is hosted in the lower and middle members of the Abrigo formation.
Moderate to intense calc-silicate alteration including garnet, epidote, and diopside are common in various assemblages, most intense calc-silicate alteration in the Lower and Middle Abrigo formations. Pervasive quartz veining occurs in both the Abrigo Formation and underlying Bolsa Quartzite throughout the Johnson Camp Mine area. Quartz vein orientations are typically sub-parallel to the stratigraphic units.
Alteration
Moderate to intense calc-silicate alteration of the stratigraphic units at Johnson Camp is widespread throughout the property, especially in the Cambrian Abrigo formation. Calc-silicate minerals including garnet, epidote, and diopside are common in various assemblages which are primarily controlled by protolith mineralogy and secondarily controlled by proximity to structures. The Middle and Lower sub-units of the Abrigo formation contain the most intense calc-silicate alteration in the area. In the Middle Abrigo Formation, brown-tan garnet and epidote alteration is consistent and diagnostic of the unit. In the Lower Abrigo Formation, the rock is dominantly altered to dark grey to black hornfels with interbedded sub-units containing diopside-rich and/or garnet-epidote lenses similar to alteration in the Middle Abrigo Formation. Pervasive quartz veining occurs in both the Abrigo Formation and underlying Bolsa Quartzite throughout the Johnson Camp Mine area. Quartz vein orientations are typically sub-parallel to the stratigraphic units. Distinctive vein halos containing coarse muscovite can be observed in certain areas of the property, especially in the Bolsa Quartzite at the Copper Chief Pit.