The Copperstone Project is wholly owned by Minera Alamos Inc. via Minera’s 100% ownership of American Bonanza.
In October 2024, Minera Alamos Inc. announced the acquisition of all shares of Sabre Gold Mines Corporation and its subsidiary American Bonanza through a plan of arrangement under British Columbia law.
In January 2025, the shareholders of American Bonanza approved the arrangement at a special meeting.
In February 2025, the Supreme Court of British Columbia gave its final approval for the transaction.
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Summary:
Deposit Type
The Copperstone deposit is presently best described as a mid-Tertiary, detachment-fault-related gold deposit. Detachment faults are low-angle (up to 30°) normal faults of regional extent that have accommodated significant regional extension by upward movement of the footwall (lower-plate) producing horizontal displacements on the order of tens of kilometers. Common features of these faults are supracrustal rocks in the upper-plate on top of lower-plate rocks that were once at middle and lower crustal depths, mylonitization in lower-plate rocks that are cut by the brittle detachment fault, and listric and planar normal faults bounding half-graben basins in the upper plate (Davis and Lister, 1988).
Mineralization
Gold mineralization at Copperstone occurs in the hanging wall of the Moon Mountain detachment fault, which has not been penetrated in drilling to date. Gold mineralization is largely restricted to the immediate vicinity of the Copperstone fault (also referred to as the Copperstone shear or the Copperstone structure), a moderately northeast-dipping, semi-planar zone of shear which is interpreted as a listric splay of the Moon Mountain detachment, and which has hosted the bulk of the gold historically produced from the Copperstone mine.
The Copperstone fault strikes about N30° to 60°W and dips from 20° to 50° to the northeast. The associated brecciated fault zone ranges from 45 ft. to 180 ft. in width with characteristic fault gouge, multiphase breccia textures, shear fabric, and intense fracture sets across this width (MDA, 2000). The Copperstone fault appears to be a brittle deformation feature situated within the extremely deformed upper plate volcanic sequence. The fault presents strong evidence of shearing, with schistose textures and conjugate sets of planar and curved faults indicated by fault gouge. Brecciation is observable in the open pit, as are steeply northeast dipping, northwest-striking fractures and narrow shear zones. Mineralization is known to occur in association with both the primary Copperstone listric fault as well as high-angle, secondary fault structures. All mineralization appears to be cut off at the southeastern edge of the pit by a northeast-striking fault that dips to the southeast. Most of the fractures in the volcanic sequence are highly irregular and discontinuous, but the Copperstone structure has remained a dependable target for exploration and mining.
Conceptual geologic model interprets the Copperstone structure as part of a detachment fault system related to regional mid-Miocene extension. More recently, Strickland et al. (2017) have recognized late Laramide detachment related to magmatism and the denudation of a Cretaceous subduction complex found across southern Arizona and California. Regardless of the age of the deformation, detachment faulting with an upper-plate-to-the-east sense of motion is presently considered the primary control/conduit for mineralization. The mineralized Copperstone fault is continuously present across the pit area from the A, B and C zones and may extend even farther south across the sparsely drilled South zone. It appears to break down or splay upon entering the D zone and there are indications of some up-dip flattening in the northern C zone.
A, B, and C Zones
Mineralization in the A, B, and C zones occurs along the primary Copperstone fault as well secondary structures within the zone of shear. Underground mapping has shown a number of steeper northwest-trending faults and fractures that localize alteration and mineralization in and around quartz-Fe oxide +/- Cu oxide veins. Observations show that where such high-angle structures intersect the low-angle (Copperstone fault) structures, a favorable site is prepared. Where the Copperstone listric fault is disrupted, a dilatant zone may occur, resulting in higher grade and thickness of the gold mineralization.
Similarly, there are northeast-trending faults which appear to offset and localize mineralization, resulting in mineralized shoots at intersections with the Copperstone fault. These northeast-trending faults occur as thin to wide crushed zones that may capture a drill string resulting in exaggerated mineralization widths. This can especially be the case where the drill pattern is based on a southwest drillhole orientation. Long intervals of elevated gold values in quartz latite, without continuity to nearby holes, suggest such high-angle controls.
D Zone
The D zone contains large imbricate slices of interbedded limestone and sandstone, of which the limestones have been largely replaced by specularite, earthy hematite and silica. In many drillholes, silica-magnetite-specularite-chlorite replacement bodies occur in two limestone layers of variable thickness, but generally no more than 5-10 ft. In some locations iron oxides form a matrix in silicified limestone but nearby there may be evidence for direct replacement of limestone by iron oxides. It is possible that some of the silicified limestone is actually a pure white quartzite that has been brecciated. This would mean that silicification does not precede iron-oxide introduction.
Elevated gold grades are associated with the limestone replacement bodies over areas of significant size, likely due to the extreme distortion and reactivity of the limestone. The slices of this sedimentary package have dimensions of up to tens to hundreds of feet in strike length and tens of feet of thickness. The imbricate slices are conformable to the Copperstone shear, having been caught up in the shearing with local rotation, tension gashes and associated deformation. This sedimentary package is located between hanging wall volcanic rocks and footwall phyllite. These sedimentary rocks are absent to the southeast in the Copperstone C, B and A zones.
The upper and lower contacts of the limestone replacement bodies are almost always tectonic. The upper contact with the volcanic rocks is also mostly tectonic but, in some locations, there is no evidence of shearing. The age of the limestone is also in doubt. It has been assumed as Triassic previously, but some are now suggesting that it is Permian in age and related to the Kaibab Limestone on the Colorado Plateau to the north. The interbedded nature of limestone with quartzite supports this idea, but the relationship to the adjacent phyllites is problematic.
Immediately north of the D zone is a northeast-trending fault zone which apparently terminates the Copperstone fault and associated secondary structures. Whether the Copperstone fault is offset or actually terminated by this fault is presently unknown, but it appears that the sedimentary sequence thickens considerably and may not be penetrated by the Copperstone fault.