Santa Eulalia Mining District, Aquiles Serdán Municipality, Chihuahua, Mexicoi

Regional Level Types
Santa Eulalia Mining District	Mining District
Aquiles Serdán Municipality	Municipality
Chihuahua	State
Mexico	Country

The Santa Eulalia Mining District lies in central Chihuahua, Mexico at latitude 28o 35' N; longitude 105o 50' W; about 360 km south of El Paso, Texas and 23 km east of Chihuahua City (Fig. 1). The district occupies the approximate center of the north-northwest elongate, fault-bounded Sierra Santa Eulalia (a.k.a. Sierra Santo Domingo) whose peaks rise up to 700 m above the surrounding plains. Maximum elevations exceed 2400 m and the numerous deep canyons carved into the limestone and volcanic rocks of the range create a very rugged topography. Santa Eulalia has been in nearly continuous production for over three centuries (1703-present) and ranks as one of Mexico's chief silver and base metal producers with over a half billion troy ounces of silver and nearly 6 million tonnes of lead and zinc recovered. The City of Chihuahua was built by Spanish pioneers on the riches emanating from Santa Eulalia over the first 200 years of mining and, although modern industry now dominates Chihuahua's economy.

In a regional geological and mineralogical perspective, Santa Eulalia is the largest of a number of similar Carbonate Replacement Deposits that occur in a 2200 km long belt running from Hidalgo State to the Chihuahua-U.S.A. border…and into the USA (Megaw et al., 1988). This belt of deposits includes many of Mexico’s most prolific specimen-producing mines such as: Ojuela, Naica, Concepcion del Oro, Los Lamentos, San Carlos, San Pedro Corralitos, Charcas and Sabinas-San Martin. That these deposits are prolific specimen producers stems from aspects of their primary genesis and subsequent oxidation that create abundant open space during times when crystal growth potential is high. Additionally, the largest Carbonate Replacement Deposits characteristically underwent multiple stages or pulses of mineralization and oxidation, which results in mineralogical overprinting and the creation of a wide range of pseudomorphs. Santa Eulalia is especially well endowed in this regard.

The Sierra Santa Eulalia consists of Cretaceous carbonate and evaporite strata deformed into a broad, north-northwest-trending, doubly-plunging anticline with generally gentle dips. These rocks were subsequently deeply eroded and unconformably buried by a southward-thickening succession of early- and mid-Tertiary volcaniclastic and caldera-related volcanic rocks. Pre and intra-mineral intrusive dikes and sills are important ore localizers and mineralization is closely linked in time and space to distinctive felsite intrusions. Post-mineral faulting or deformation is minimal, so erosion and oxidation from meteoric waters is all that has happened to the ores since their deposition.

The mining district is divided into the West and East Camps, based on a combination of geography, production and style of mineralization. The West Camp (a.k.a. The Main Mineral Zone; Prescott, 1916 and Hewitt, 1968) lies on the western flank of the range and is characterized by massive sulfide manto and chimney orebodies with local, high-level iron-calcic skarns. The East Camp (a.k.a. the San Antonio mine area) lies on the eastern fringe of the range and is characterized by bilaterally symmetrically zoned, intrusion-cored skarns with peripheral massive sulfide manto bodies. The 2.5km wide intervening zone, known as the Middle Camp, contains minor mineralization and saw limited production, but is generally considered barren. The ultimate source of the district mineralization is actively being sought, but remains elusive.

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