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El Barqueno |
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Jalisco, Mexico |
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Au Ag Cu Zn Pb
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Super Porphyry Cu and Au
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The polymetallic (Au-Ag-Cu-Zn-Pb) low sulphidation epithermal veins of the El Barqueño district are located in the Guachinango municipality, about 150 km west of Guadalajara in the State of Jalisco, west-central Mexico.
These deposits comprise around 30 Au-Ag-Cu-Zn-Pb veins hosted by a volcano-plutonic assemblage which belong to the Lower Volcanic Supergroup of the southwestern part of the Sierra Madre Occidental, within the Jalisco block. The volcanic rocks of the Lower Volcanic Supergroup are the dominant lithology in the area and their stratigraphy comprises, from bottom to top, andesites, porphyritic andesites and andesitic tuffs. These rocks are considered to be Paleocene to Oligocene in age and are strongly propylitised throughout the district. Porphyritic andesites are the most common host for the epithermal vein mineralisation. The volcanic rocks were intruded by plutons, ranging from diorites or granodiorites and monzogranitesto tonalites dated at between 97.6 and 40.8 Ma.
The veins trend from 45 to 100°,and dip to the southeast and south, steepening with depth. The maximum strike length of the veins at El Barqueño is about 5 km, and the maximum vein thickness is about 10 m (averaging 2 to 3 m), narrowing with depth. An adularia separate from crustiform quartz bands of stage 2 has been dated by 40Ar/39Ar geochronology at 57.91 ± 0.44 Ma (isochron age).
The paragenetic sequence indicates two main mineralisation stages. Stage I occurs as breccias with base metal sulphides and virtually no gold or silver. Stage 2 consists of crustiform quartz bands that form symmetrical vein fillings and contain the precious metals. Rhombohedral adularia crystals and quartz pseudomorphs after bladed calcite are widespread in stage 2, providing evidence for boiling. Gold- and silver-bearing metallic minerals locally precipitated directly on adularia crystals, an association indicating boiling as the main mechanism of metal deposition. Conductive cooling and mixing also may have been important.
Intensive mining began soon after the Spanish occupation, with the first mines in the Guachinango district dating from around 1550. Actual production figures are not available in the sources consulted for this record.
The most recent source geological information used to prepare this decription was dated: 2006.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Camprubi A, Gonzalez-Partida E, Iriondo A and Levresse G, 2006 - Mineralogy, fluid characteristics, and depositional environment of the Paleocene epithermal Au-Ag deposits of the El Barqueno district, Jalisco, Mexico: in Econ. Geol. v101 pp 235-247
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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