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Mineral Exploration for Gold-Bearing Levels in the Central-Western Zone of Asturias (Spain)
Journal of Geochemical Exploration, 32 (1989) 409-410
409
ElsevierSciencePublishersB.V., Amsterdam-- Printed in The Netherlands
Mineral exploration for gold-bearing levels in the central-western zone of Asturias (Spain) J. LOREDO1,J. GARCIAIGLESIAS1and F. RUIZ2 ' Escuela de Minas, Univ. de Oviedo, Independencia 13, 33004- Oviedo, Spain 2 IMINSA, Marquis de Teverag 2, 33005 - Oviedo, Spain
(ReceivedJanuary 15, 1988;revisedand acceptedSeptember6, 1988)
ABSTRACT
In the central-western Zone of Asturias, northern Spain, there are many Roman surface workings for Au. These deposits are associated with certain predominantly quartzitic or dolomitic strata of Early to Middle Cambrian age or with granodiorites. Mineral exploration combining geochemical and geological techniques has been applied to several mineralized areas containing carbonate-rich formations (Navelgas, Abaniella and Begega deposits), quartzite or sandstone stata (Antohana and Castro de la Grueba deposits), or igneous rocks (Carl~s and God~n deposits). The host rocks show evidence of different types of epigenetic alteration: dolomitization, sericitization, chloritization, or silicification. Sometimes skarn is formed (Carl~s, God~n ). Silicification is important near fractured zones, where the presence of quartz veins a few millimetres thick is common. On a regional scale, a structural analysis of the fracture network confirms the existence of two important fracture systems (N 40 °E and N 110 °E) with which mineralization is associated, at least locally on a deposit scale. Frequently, the Au is associated with quartz veins having these orientations. In addition, the locations of some igneous bodies are controlled by major fractures related to these systems. Gold particles are associated with quartz or secondary Fe oxides in rocks that have been subjected to intense supergene alteration, whereas, in areas of less oxidized mineralization associated with igneous intrusions and skarn formation (Carl~s, God'n), the association of Au and sulfides (especially arsenopyrite) is characteristic of the quartz veins. In areas where drainage cuts across the mineralized structural lineaments, stream-sediment surveys proved very useful. Gold particles between 10 and 20 microns (and occasionally reaching 50 microns) are frequently found in the panned, heavy-mineral fraction. The number of Au particles per sample decreases with distance from mineralized sources. 0375-6742/89/$03.50
© 1989ElsevierSciencePublishers B.V.
410
Principal-component analysis of the multi-element rock geochemical data (Ag, As, Au, Ba, Bi, Cu, Hg, Mn, Mo, Pb, Sb, Te, Zn) in 84 samples of host rock from four areas with Au mineralization (Navelgas, Abaniella, Begega, Antofiana) shows that Au is associated with As and Hg; thus, Au, As, and Hg are the best elements to use in Au prospecting using rock samples. The other elements (Ag, Ba, Bi, Cu, Mn, Mo, Pb, Sb, Te, Zn) show no association with Au and are not useful in lithogeochemical prospecting for these deposits. A relationship between fracturing and mineralization is inferred, and the highest Au content is associated with the highest density of quartz veins in the rock. A total of 136 soil samples were collected along four traverses (Navelgas, Abaniella, Begega, Antofiana) that were laid out up-hill from mineralized areas in order to prevent contamination from old open-pit workings. These samples were analyzed for Ag, As, Au, Ba, Bi, Cu, Hg, Mn, Mo, Pb, Sb, Te and Zn. In contrast to the Au-As-Hg geochemical association seen for the rock samples, principal-component analysis of the soil geochemical data shows a poor correlation between Au and all of the other elements. No spatial correlation of Au and other element anomalies was evident; thus, the elements analyzed with Au are not useful indicator elements in soil surveys in these areas.
409
ElsevierSciencePublishersB.V., Amsterdam-- Printed in The Netherlands
Mineral exploration for gold-bearing levels in the central-western zone of Asturias (Spain) J. LOREDO1,J. GARCIAIGLESIAS1and F. RUIZ2 ' Escuela de Minas, Univ. de Oviedo, Independencia 13, 33004- Oviedo, Spain 2 IMINSA, Marquis de Teverag 2, 33005 - Oviedo, Spain
(ReceivedJanuary 15, 1988;revisedand acceptedSeptember6, 1988)
ABSTRACT
In the central-western Zone of Asturias, northern Spain, there are many Roman surface workings for Au. These deposits are associated with certain predominantly quartzitic or dolomitic strata of Early to Middle Cambrian age or with granodiorites. Mineral exploration combining geochemical and geological techniques has been applied to several mineralized areas containing carbonate-rich formations (Navelgas, Abaniella and Begega deposits), quartzite or sandstone stata (Antohana and Castro de la Grueba deposits), or igneous rocks (Carl~s and God~n deposits). The host rocks show evidence of different types of epigenetic alteration: dolomitization, sericitization, chloritization, or silicification. Sometimes skarn is formed (Carl~s, God~n ). Silicification is important near fractured zones, where the presence of quartz veins a few millimetres thick is common. On a regional scale, a structural analysis of the fracture network confirms the existence of two important fracture systems (N 40 °E and N 110 °E) with which mineralization is associated, at least locally on a deposit scale. Frequently, the Au is associated with quartz veins having these orientations. In addition, the locations of some igneous bodies are controlled by major fractures related to these systems. Gold particles are associated with quartz or secondary Fe oxides in rocks that have been subjected to intense supergene alteration, whereas, in areas of less oxidized mineralization associated with igneous intrusions and skarn formation (Carl~s, God'n), the association of Au and sulfides (especially arsenopyrite) is characteristic of the quartz veins. In areas where drainage cuts across the mineralized structural lineaments, stream-sediment surveys proved very useful. Gold particles between 10 and 20 microns (and occasionally reaching 50 microns) are frequently found in the panned, heavy-mineral fraction. The number of Au particles per sample decreases with distance from mineralized sources. 0375-6742/89/$03.50
© 1989ElsevierSciencePublishers B.V.
410
Principal-component analysis of the multi-element rock geochemical data (Ag, As, Au, Ba, Bi, Cu, Hg, Mn, Mo, Pb, Sb, Te, Zn) in 84 samples of host rock from four areas with Au mineralization (Navelgas, Abaniella, Begega, Antofiana) shows that Au is associated with As and Hg; thus, Au, As, and Hg are the best elements to use in Au prospecting using rock samples. The other elements (Ag, Ba, Bi, Cu, Mn, Mo, Pb, Sb, Te, Zn) show no association with Au and are not useful in lithogeochemical prospecting for these deposits. A relationship between fracturing and mineralization is inferred, and the highest Au content is associated with the highest density of quartz veins in the rock. A total of 136 soil samples were collected along four traverses (Navelgas, Abaniella, Begega, Antofiana) that were laid out up-hill from mineralized areas in order to prevent contamination from old open-pit workings. These samples were analyzed for Ag, As, Au, Ba, Bi, Cu, Hg, Mn, Mo, Pb, Sb, Te and Zn. In contrast to the Au-As-Hg geochemical association seen for the rock samples, principal-component analysis of the soil geochemical data shows a poor correlation between Au and all of the other elements. No spatial correlation of Au and other element anomalies was evident; thus, the elements analyzed with Au are not useful indicator elements in soil surveys in these areas.