The gold area of Jales (northern Portugal) |
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| Authors: | JM Cotelo Neiva AMR Neiva |
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| Institution: | Department of Mineralogy and Geology, University of Coimbra, 300 Coimbra, Portugal |
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| Abstract: | The hydrothermal gold quartz veins of Jales cut Hercynian granitic rocks, Pre-Ordovician, Ordovician and Silurian schists. They occur along Hercynian NNE-SSW, NE-SW and WNW-ESE faults and are probably related to the Jales granite. Some are over 2 km long and have a thickness of 0.02–2 m. The only exploited quartz veins are from Campo and Desvio which contain several ore-shoots (25t Au exploited since 1933). The veins from Jales area also have good Au reserves. Quartz and arsenopyrite dominate in the gold quartz veins with a banded structure. Electrum and gold are included in sulphides, sulphosalts and quartz and also in veinlets cutting these minerals. Silver occurs in electrum, argentite, galena, freibergite and polyargyrite. Several minerals were analysed by electron microprobe. The primary minerals, some showing recurrences, belong to six paragenetic stages formed between 550 and 30°C and separated by faulting. |
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