Projects

The Guigui Project and the Santa Eulalia Mining District lies in central Chihuahua Terrane, which is underlain by Precambrian continental crust overlapped by Lower Cretaceous sedimentary rocks and Tertiary volcanic rocks.

The Sierra Santa Eulalia is a horst block bounded by steeply dipping normal faults on both the east and west sides of the range. The body of the range is composed of lower Cretaceous limestone and underlying evaporites, which were folded into a broad doubly plunging anticline with a NNW-SSE trending axis and gentle dips.

Limestone outcrops throughout the northern portion of the range but becomes covered by an increasingly continuous blanket of lower Tertiary volcanic and volcaniclastic rocks towards the south. Erosional windows of lime- stone are locally exposed through these volcanic rocks. The lower Tertiary section continues southward until it be- comes buried under a thick package of mid-Tertiary ash-flow tuffs and basalts, erupted from the resurgent Santo Domingo Caldera, which occupies the southern half of the range. This southern portion of the sierra consists almost entirely of intracaldera volcanic rocks.

The Santa Eulalia District is the largest known Carbonate Replacement Deposit (CRD) in Mexico and the largest among the CRDs that define a belt running from Hidalgo to near the Chihuahua-U.S.A border (Table 1).

Carbonate Replacement Deposits are Phanerozoic, high-temperature (>250 °C) deposits that comprise major pod, lens, and pipe-shaped Pb-Zn-Ag-Cu-Au-sulfide orebodies that cut across their host carbonate rocks. They are dominantly composed of a simple assemblage of galena, sphalerite, chalcopyrite, arsenopyrite, pyrite and/or pyrrhotite with subordinate carbonate, sulfate, fluorite and quartz gangue. A model of the CRD was established and developed by Dr. Peter Megaw from his dissertation studies at the Santa Eulalia.

The mining district is divided into three camps—West, East and Middle Camps. Guigui Project lies immediately to the south of these camps:

• West Camp (SEWC) - Principal past producers in the camp are Grupo Mexico’s Buena Tierra Mine and MINA- MEX’s Potosi Mine.
• East Camp (SEEC) - Production is dominated by Grupo Mexico’s San Antonio Mine, which is currently in production.
• Middle Camp (SEMC) - The 2.5-km zone between SEWC and SEEC; Contains numerous mineralized showings and small mines but has not been systematically explored.

The East and West Camps contain continuous, zoned mineralization and alteration closely associated in time and space to groups of apparently identical felsite intrusions. Although the mineralization in the two camps does not overlap in space, both appear to have resulted from the evolution of persistent, pulsating, hydrothermal systems. The morphology of the felsites coupled with mineralogical, metals content, metal ratios, sulfur isotope, and mineralization style, strongly indicates a common hydrothermal source for the two camps. This source appears to lie between the two camps, immediately north of the Santo Domingo caldera (Megaw, 1990).