Geochemistry, Mineralogy and Genesis of Newly Discovered Gossanite-Like Ore Bodies Associated with Microbial Involvement in the Zagros Ophiolites of Iraqi Kurdistan.
Abstract
We report here on the discovery of a gossanite-type hematite and magnetite ore, associated with sulphide mineralizations in the Rayat area of Iraqi Kurdistan. Detailed petrographical, mineralogical, and geochemical data defined the features of the gossanite, providing an assessment of the observed mineralizations and their relation to hydrothermal process, as well as a basis for an initial genetic model. In the uppermost part, extensive hard and compact Fe-rich layers occur representing jasperite lithofacies, being composed of iron-oxides, quartz/chalcedony, chlorite and to lesser amounts of spinels. Interestingly within the upper parts of the jasperite horizon, millimetre-thick layered iron-silicates alternations were also visible and comparable to Banded Iron Formation. Below the jasperite the Oxidized Mineralized Zone (OMZ) is developing, being very rich in iron oxides (up to 70%), chlorite, and quartz with some minor content of spinel. The lowermost part is a Reduced Mineralized Zone (RMZ) composed of silica, pyrite, chalcopyrite, pentlandite, Ni-chlorite, and siderite. A Transition Zone, approximately 1 m thick, in between the OMZ and RMZ, contains chlorite, Fe-oxides, quartz, and partially altered sulphide minerals. The potential economic importance of the ore body in addition to Fe, is the Silver-Nickel (Ag-Ni) and Cobalt (Co) mineralization that it contains, with silver mostly occurring as exsolution inside chalcopyrite within sulphidic-cherts lithofacies. A thin coal lensoid bed having a field association to the gossanite strata, being quite peculiar, and probably explained as being part of the Ophiolitic Mélange, provides some initial clues for the thermotectonic evolution of the studied strata.
SEM studies of the various gossanite horizons indicate the occurrence of well-preserved biosignatures, represented by rich and well-embedded microbial assemblages pertaining mostly to coccoidal, chain-like, rods, and filamentous bacteriomorphs. The overall data of this research suggest that Rayat Gossanite was formed near to a seafloor environment by a combination of hydrothermal alteration of serpentinites, accompanied on the upper parts by sedimentary deposition of Fe-Si-exhalative along with olistostromatic brecciated facies.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMV007.0003P
- Keywords:
-
- 0999 General or miscellaneous;
- EXPLORATION GEOPHYSICS;
- 3665 Mineral occurrences and deposits;
- MINERALOGY AND PETROLOGY;
- 7218 Lithosphere;
- SEISMOLOGY;
- 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICS