| alteration: | IRREGULAR ALTERATION HALOS CONSIST OF MARMORIZATION, BLEACHING, LOCAL SILICIFICATION, AND EPIDOTIZATION. SILICATE ALTERATION OCCURS IN THE TACTITE DOME, AND THE OUTER TACTITE ZONE CONTAINS STRONG EPIDOTIZATION, CHLORITIZATION AND LESSER TALC. MARMORIZATION OCCURS ADJACENT TO CHIMENYS, DIKES, THE TACTITE BODY, AND MINERALIZED FRACTURES. THE DIMENSION OF ITS HALO VARIES FROM LESS THAN ONE CENTIMETER TO A MAXIMUM OF A FEW TENS OF METERS (60M). DIFFUSE LOCAL SILICIFICATION, AND QUARTZ IN FRACTURES ARE ABUNDANT NEAR THE ORE. WITH THE EXCEPTION IF MARMORIZATION AND BLEACHING, ALTERATION HALOS ARE SO LOCAL AND NARROW THAT THEY ARE OF LITTLE USE AS GUIDES FOR MINERALIZATION. |
| Structure: | SURFACE EXPRESSION OF OREBODIES RANGES FROM NONE TO VERY LIMITED. OXIDIZED ZONES OR SCARCE CALCITE BRECCIAS OR OREBODIES. COMMONLY, THIN (LESS THAN 1 MM. TO A FEW CENTIMETERS) CALCITE-HEMATITE-MANGANESE OXIDE MICROVEINLETS COMPOSE THE STOCKWORKS OR ARE IRREGULARLY DISTRIBUTED ABOVE MINERALIZED ZONES., STRUCTURALLY, LA ENCANTADA LIES ON THE SOUTHWESTERN FLANK OF THE NW-SE-TRENDING SIERRA DE LA ENCANTADA ANTICLINORIUM. THE BEDS ON THE FLANKS OF THE SIERRA DE LA ENCANTADA DIP 30-40 DEGREES WITH LOCAL VERTICAL AND OVERTURNED STRATA. IN THE MINE AREA, THE BEDS DIP FROM 20-30 DEGREES W. BLOCK FAULTING CUTS THE ANTICLINE STRUCTURES OF SIERRA DE LA ENCANTADA. A REGIONAL N26W FAULT, TRACEABLE FOR 38 KM, CUTS THE ANTICLINORIUM SW OF THE MINE. THIS FAULT POSSIBLY REFLECTS REACTIVATION OF PALEOZOIC BASEMENT FAULTS DURING LARAMIDE TIME AND MAY HAVE CONTROLLED THE EMPLACEMENT OF THE GRANODIORITE BODY. A SIMILAR STRUCTURAL SETTING HAS BEEN INVOKED TO EXPLAIN THE LOCALIZATION OF SEVERAL MINERAL DEPOSITS ALONG THE CHIHUAHUA TROUGH. MOST OF THE FAULTS ARE NORMAL, AND THE MAIN SYSTEMS TREND N15-30W AND N50-80E. BOTH SYSTEMS POSTDATE FOLDING AND PREDATE MINERALIZATION ALTHOUGH THE EXACT RELATIONSHIP BETWEEN THEM IS UNCLEAR. NORTHEAST-TRENDING FRACTURES APPEAR TO BE OLDER THAN THE NW-TRENDING FAULTS. MULTIPLE PHASES OF FRACTURING ASSOCIATED WITH UPLIFT AND IGNEOUS INTRUSIONS ADD COMPLEXITY TO THE STRUCTURAL REGIME. WITH THE EXCEPTION OF THE REGIONAL LA ENCANTADA FAULT, THE N15-30W SYSTEM APPEARS TO BE SHALLOW AND PROBABLY INDICATES SEPARATE FAULTING AND FRACTURING PHASES WHICH WERE ACTIVE AFTER FOLDING AND CONTINUED AFTER INTRUSION AND MINERALIZATION. IN THE MINE AREA, TWO GRABENS BOUNDED BY THE ROMO-MARIA ISABEL AND SAN JUAN-SAN JOSE FAULTS CONTAIN THE CENTRAL OREBODIES (LA PRIETA-LA ESCONDIDA). |
| References: |
- Deposit:: DIAZ-UNZUETA, R., 1986, GEOLOGY AND MINERALIZATION OF THE LA ENCANTADA SILVER-LEAD DISTRICT, COAHUILA, MEXICO; IN, CLARK, K.F., MEGAW, P.K.M., RUIZ,J., LEAD-ZINC-SILVER CARBONATE-HOSTED DEPOSITS OF NORTHERN MEXICO, GUIDEBOOK FOR FIELD AND MINE EXCURSIONS: SOCIETY OF ECONOMIC GEOLOGISTS, NOVEMBER 13-17, 1986, PP. 311-323.
- Deposit:: LOZEJ, G.P., AND BEALES, F.W., 1977, STRATIGRAPHY AND STRUCTURE OF LA ENCANTADA MINE AREA, COAHUILA: GEOLOGICAL SOCIETY OF AMERICA BULLETIN, V. 88, P. 1793-1807.
- Deposit:: LUJAN, G.M.A., 1975, GEOLOGIA E INTERPRETACION DE LOS CUERPOS PLOMO-PLATA DE LA ENCANTADA, COAHUILA: AIMMGM, MEMORIA XI CONVENCION NACIONAL, P. 531-576.
- Deposit:: MINING MAGAZINE, 1980, LA ENCANTADA: MINING MAGAZINE, JANUARY 1980, P. 12-23.
- Deposit:: SMITH, C.I., 1971, LOWER CRETACEOUS SEDIMENTATION AND TECTONICS OF THE COAHUILA AND WEST TEXAS PLATFORMS: WEST TEXAS GEOLOGICAL SOCIETY PUBL. 71-59, P. 75-82.
- Deposit:: TREJO, P., 1983, EL PROCESO SUPERGENICO EN LA ENCANTADA, COAHUILA: MEMORIA DE LA XV CONVENCION NACIONAL AIMMGM, 1983.
- Deposit:: CAMPA, M.F., AND CONEY, P.J., 1983, TECTONO-STRATIGRAPHIC TERRANES AND MINERAL RESOURCE DISTRIBUTIONS IN MEXICO: CAN. JOUR. EARTH. SCI., VOL. 20, P. 1040-1051.
- Deposit:: CONEY, P.J., AND CAMPA, M.F., 1984, LITHOTECTONIC TERRANE MAP OF MEXICO: U.S.G.S. OPEN-FILE REPORT 84-523 (MAP).
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