Geology of Ore Deposits最新文献

Abstract

Copper-rich deposits associated with magmatism at the Oued Belif -Ain El Araar area in North-western Tunisia fit into the geodynamic framework of the Tell-Rif orogenic belt of North Africa that extends westward to the Betic Cordilleras in Spain at the african and european plate boundary. The deposits have been considerably studied. However, the prevailing conditions of pressure, volume, temperature and composition (P-V-T-X) of the mineralizing fluids are still elusive. In this study, three types of fluid inclusions were distinguished for the mineralized facies: primary polyphase brine inclusions (Type I: liquid + vapor + halite + sylvite), primary sylvite (Type II-a: liquid + vapor + sylvite) and halite (Type II-b: liquid + vapor + halite) bearing inclusions and biphasic secondary vapor-rich and liquid-rich inclusions (Type III: liquid + vapor). Raman spectroscopy show that Type I and II a-b inclusions are in the CO₂–H₂O–NaCl–KCl, CO₂–H₂O–NaCl and CO₂–H₂O–KCl systems, whereas Type III pertains to the CO₂–H₂O system. Estimations of Pressure-Temperature fluid trapping conditions, for all mentioned inclusions, demonstrate a physicochemical fluid evolution from the highest temperature brine inclusions (T_t = 500°C; P_t = 980 bars), related to the porphyry phase, to the low temperature biphasic inclusions (T_t = 131°C; P_t = 221 bars) related the latest epithermal phase .The coexistence of liquid-rich and vapor-rich inclusions homogenizing at lower temperatures, confirms the establishment of boiling conditions responsible of Au–(Ag) enrichment in the last mineralizing phases. Comparable temperature conditions in similar magmatic related deposits are also mentioned in southern Spain (Rodalquilar gold mine, e.g., Arribas et al., 1995) where the mineralizing fluid temperatures mentioned vary from 175°C for epithermal deposits to more than 400°C for porphyry ones. The geochemical behavior of trace element indicates positive anomalies in mobile elements (hygromagmaphiles), those linked to Au, granitophiles (mainly W and Mo) and chalcophiles indicating a supply of metals of deep origin and mineralizing fluids with marked magmatic differentiation.

Abstract

The present paper considers petrographic and geochemical features of rocks of the Tigrinoe and Zabytoe stocks, provides their mineral composition, the results of the detailed study of micas and mineral-forming inclusions in quartz. It is shown that the development of ore-magmatic systems (OMSs) of the Zabytoe and Tigrinoe deposits is associated with the same rare-metal Li–F melts. It is confirmed that granitoids of the Tigrinoe stock can be considered as more differentiated analogs of granitoids of the Zabytoe stock. New data concerning the differences in the history of the magmatic stage of development of the OMSs of these deposits are presented. The evolution of melts of both deposits took place at high fluid pressure. Differences in the scale of ore mineralization of the two RMSs under consideration could be due to different fluid regime of magmatic sources evolution and more significant participation of transmagmatic fluid flows in the development of the Tigrinoe OMS.

Abstract

As a method for discovering the footprint of concealed iron ore enrichments, oxygen isotopes have revealed hydrothermal fluid sources and processes in Banded Iron Formation (BIF)-hosted iron ore provinces worldwide. This paper reviews the role oxygen isotopes play in exploring BIF-hosted iron ore bodies and discusses their application in southern Cameroon’s Precambrian mineral belt as an auxiliary exploration technique. Oxygen isotope analysis of iron ore species (e.g., BIFs, itabirites, and jaspilites) showed that the least altered BIFs had higher δ¹⁸O values than enriched ores. In the Nyong complex BIF sequence of southern Cameroon, δ¹⁸O_mag values range from –3 to –1.8, while δ¹⁸O_qtz values range from 6.8 to 10.6, indicating a discernible shift between the δ¹⁸O_mag-qtz values. Much higher δ¹⁸O_mag values (2.89 to 9.30‰) have been observed for magnetite gneisses suggesting an evolved magmatic-hydrothermal fluid source. Quartz veins associated with early-stage hematite ores in the adjacent Ivindo basement complex display higher δ¹⁸O values (4.7 to 8.1%) than those associated with late-stage magnetite ores (–2.3 to –1.5%). It is evident from these values that there is an isotopic shift between early-stage and late-stage iron ores, supporting the relevance of oxygen isotope to understanding iron ore signatures within the NW margin of the Congo craton. However, since the Congo Basin is characterised by inaccessible equatorial vegetation cover and lacks superficial exposures, high-precision oxygen isotopes (δ¹⁸O and δ¹⁷O) in conjunction with other isotopic techniques (e.g., δ⁵⁶Fe) and lithogeochemistry, will be more useful in constraining the isotopic signature of the BIF mineralisation.

An Erratum to this paper has been published: https://doi.org/10.1134/S1075701523370018