Status: Available for Option
The primary targets at La Union are precious metal-enriched, carbonate replacement deposits. The secondary target is a concealed, orogenic gold deposit hosted in crystalline basement rocks.
Location and Setting
The La Union project is located along the southeastern terminus of the Sierra el Viejo, approximately 50 kilometers southwest of the city of Caborca, Sorona, Mexico.
The property consists of two claims, totalling 11,776 hectares. Internal, third party claims cover the La Union and La Famosa mine workings.
Geology and Mineralization
Bedrock within the Sierra el Viejo comprises a folded and faulted sequence of upper Proterozoic / lower Paleozoic carbonate and quartzite, intruded by diorite of presumed Cretaceous /Tertiary age. Mineralization at La Union is preferentially hosted within a distinctive interval of intimately interbedded quartzite and stromatolitic dolomite which occurs low in the stratigraphy, along the eastern margin of the range. Fresh, undeformed diorite intrudes the basal sedimentary sequence over much of the project area. Although unmineralized, these intrusive rocks may be important as they are very similar to others in western Sonora which were typically emplaced at or near the contact between basement crystalline gneiss and overlying Proterozoic supracrustal rocks.
There are several small, historic producers located in the district. The strongest mineralization is focused within a N-S belt anchored on the south by the La Famosa Mine and on the north by La Union. Both mines exploited manto / chimney replacement bodies hosted primarily by dolomite and, to a lesser extent, quartzite. Alteration includes proximal silicification (“jasperoid”) and more distal recrystallization of host carbonate.
The auriferous character of this mineralization is exceptional with respect to other replacement type deposits in Mexico and elsewhere. La Union, the larger of the two mines, was operated during the 1950’s by a subsidiary of Penoles. The mine reportedly produced approximately one million tonnes of high grade, polymetallic oxide mineralization averaging 7-20 g/t Au, 300 g/t Ag, 10-20% Pb and 5% Zn. Mineralization at La Famosa is almost exclusively sulfide but exhibits similar geochemistry (Pb-Zn-Cu-Au-Ag-As-Sb). Records show high grade direct shipping ore from select material in 1986 grading 35 gpt Au and 800 gpt Ag.
Workings on the Millrock La Union claims consist of small prospect pits where samples of mineralized material returned anomalous gold assays. In addition, shallow placer gold workings are widespread along the La Famosa ridge, at or near the bedrock / alluvium interface. A significant portion of the projected trend of district mineralization as well as covered areas underlain by favorable lithologies lie within the claim.
The La Union claims are considered prospective for the discovery of high-grade bodies of massive, replacement-style Au-Ag polymetallic mineralization. Exploration efforts should focus on the projection of favorable structures and coincident favorable lithologies from areas of outcrop to surrounding, shallow pediment. An orientation sampling program focused on stable isotope (O,C) analyses is recommended as a means to detect blind deposits adjacent known mineralization. Geophysics and shallow RC drilling would be the best techniques for further, follow-up exploration. Standard stream sediment sampling has failed to detect any significant values, even in close proximity to well mineralized workings; an orientation survey using ultra-low detection limit analytical methods is recommended.
Agreement and Terms
Millrock controls 100% of the La Union claims, subject to production royalties of 1.5% on gold and 1% on other metals.
Millrock is currently seeking potential joint venture partners for the La Union Project. If desired, Millrock can serve as operator on behalf of an earn-in partner.
“THE TECHNICAL INFORMATION WITHIN THIS DOCUMENT HAS BEEN REVIEWED AND APPROVED BY GREGORY A. BEISCHER, PRESIDENT & CEO OF MILLROCK RESOURCES INC. MR. BEISCHER IS A QUALIFIED PERSON AS DEFINED IN NI 43-101.”