Role of magma and fluid flow processes in distribution of Cu-Ni and Platinum - Group Elements

The large layered intrusions such as the Bushveld Complex, the Duluth Complex and the Sudbury Igneous Complex are among the principal sources of Cu, Ni and Platinum Group Elements (PGE) of the world. Most of sulfide ores in these complexes are results of magmatic segregation and fractiona-tion and various models based on these magmatic processes have been used for understanding minera-logy, petrology and origin of these ores. However, recent studies on mineralized igneous complexes have also pointed out the role of physical processes during the emplacement of magma, such as interaction of magma with the footwall; fluid segregation; and superimposing hydrothermal processes in defining and modifying of features of these ores. The proposed project aims to develop a new and complex model that equivocally include segregation-fractionation and additional fluid- related processes for better understanding the behaviour and enrichment of metals in these systems on the basis of studies on mineralized intrusions of the Duluth Complex. The research will focus on the following aspects: 1. Origin, direction and turbulence of magma flow and effect of these processes on the composition of the segregated sulfide melts. 2. Partial melting processes in the footwall of intrusions and interaction of partial melts and their segregated fluids with the intrusions. 3. Contribution to the knowledge about mafic-ultramafic intrusion-related magmatic-hydrothermal systems and establishment of a model that also considers the role of fluids in distribution of Cu, Ni and PGE during crystallization of layered mafic-ultramafic complexes. 4. Establishment a model for processes leading to formation of PGE-enriched sulfide ores in the footwall of layered intrusions. 5. Providing observations and models of the geochemical behaviour of PGE in magmatic and fluid systems related to large layered mafic-ultramafic complexes. The project will be executed on the basis of cooperation between six leading scientists from the Karl-Franzens- University of Graz,Austria; the Eötvös Lornd University of Budapest, Hungary; the Natural Resources Research Institute, University of Minnesota, Duluth and the University of Nevada, Reno, U. S. A.; and will use petrography, electron microprobe analyses, geochemical assays, as well as fluid inclusion and sulfur isotope studies. The duration of the project is planned to be 3 years (2011-2014) and the proposed budget includes employment of a post-doctoral researcher at the Karl-Franzens-University of Graz.

The objective of this project was to understand the processes of Cu-Ni-Co and Platinum group elements mineralization in the Duluth mafic-ultramafic intrusion of Minnesota, USA, and the role of fluids in these processes. Such types of mineralizations are mainly found in large mafic-ultramafic intrusions such as the Bushveld Complex in South Africa; the Sudbury Igneous Complex in Canada etc. These are among the principal sources of Cu, Ni, Co and Platinum Group Elements (PGE) of the world. The Duluth Complex and associated intrusions (~1.1 Ga. old) in northeastern Minnesota, U.S.A. constitute one of the largest mafic intrusive complexes in the world, second only to the Bushveld Complex of South Africa. Cu-Ni-Co-PGE mineralization in the Duluth Complex is largely confined to the basal portions of the intrusion in contact with the country rocks which vary from metavolcanics to metasedimentary as well as granitoid rocks. Although the style of mineralization in all of the deposits is dominated by disseminated Cu-Ni sulfides, differences occur between the deposits in igneous stratigraphy, sulfide mineralogy, Cu-Ni and PGE grade, mineralization thickness, and contained tonnes. This variation is found to be due to the importance of various aspects of sulfide deposition that includes physical and chemical state of magma pulses, extent and mode of magmatic sulfide segregation and fractionation, interaction with various footwall lithologies, magmatic fluid separation and superimposing fluid/rock interaction. The mineralized intrusions of the Duluth Complex have been intersected by several thousands of meters of drillings. Results of studies of representative drill core samples suggest that the basal mineralization in the Duluth Complex was not formed by a simple magma injection and differentiation process, and therefore multiple injections of magmas with different characteristics should be considered. These differences could have resulted in the heterogeneous nature of the mineralized zone. However, not only the initial differences in the characteristics of the intruding magma batches cause the chemical and petrological differences, but sulphur isotope data suggest that these magmas have reacted with the footwall units, incorporated sulfur and some of its felsic material which is an important factor in sulfide-saturation and distribution of metals. The sulfide portion of the magma has also undergone fractionation processes that affect the local and regional mineralogy of the resultant ore deposits. The Duluth Complex is not free of overprinting hydrothermal systems that could have continuously evolved from late-stage, contaminated melts. All of these processes have crucial consequences regarding the composition of ore and the physical and chemical characteristics of the host rocks. This project has confirmed the presence of two generations of mineralizations: 1) related to the primary magmatic differentiation and 2) those transported by Cl-rich fluids and deposited at the basal zone of the complex. The project has contributed in educational, scientific and economic aspects by involving Post docs, PhDs and Master students in the project; and suggesting models of mineralization for such economically significant precious metal deposits world-wide.