Crystallization processes of Mn-columbite, Mn-tantalite, microlite, pyrochlore, wodginite and titanowodginite in highly fluxed haplogranitic melts
Dept of Earth Sciences
Niobium and tantalum are rare metals that are used in many modern technologies such as alloys, magnets, microprocessors, etc. Mn-columbite [MnNb2O6], Mn-tantalite [MnTa2O6], wodginite [Mn(Sn, Ta)(Ta, Nb)2O8], titanowodginite [MnTi(Ta,Nb)2O8], microlite [(Na,Ca)2Ta2O6(O,OH,F)] and pyrochlore [(Na,Ca)2Nb2O6(O,OH,F)] are ore grade Ta and Nb minerals whose crystallization mechanisms have been under studied. The purpose my research is to better understand the processes responsible for the formation of these different mineral phases in flux rich pegmatite melts.
In McNeil et al (2015)1, I describe a method of synthesis for Mn-columbite, Mn-tantalite, hafnon and zircon at 800-850°C. This is important because no previous method could synthesize all four of these mineral phases within the range of cold seal pressure vessels (CSPVs). In this paper, I used the electron microprobe at the Earth and Planetary Materials Analysis Laboratory here at Western University to image (Figure 1) and analyze the minerals that I synthesized, and determine their stoichiometries. The JEOL-8530F microprobe allows for analysis of very small crystals, approaching 1 µm, with excellent accuracy and precision (Figure 2).
Current research is now focusing on the crystallization mechanisms of wodginite, titanowodginite, microlite and pyrochlore, and their solubilities in flux rich pegmatite melts. I am currently using the electron microprobe to analyze pegmatite glasses that have been doped with titanowodginite (Figure 3), to determine the solubility of titanowodginite. In the future I will be creating experiments in which I will try to crystallize Mn-columbite, Mn-tantalite, microlite and pyrochlore within a pegmatite melt, by the melt coming in contact with Mn or Ca rich hydrothermal fluids. For these experiments, I will be using the microprobe to determine the phases that crystallized from the experiments, and their solubilities in the pegmatite melt.
1 McNeil, A.G., Linnen, R.L., and Flemming, R.L. 2015. Hydrothermal synthesis of columbite-(Mn), tantalite-(Mn),
hafnon, and zircon at 800–850 °C and 200 MPa. The Canadian Mineralogist (in press).
Contrasting mineralogical and geochemical characteristics of Sudburybreccia adjacent to footwall Cu-Ni-PGE sulfide deposits, Sudbury, Ontario
Dept of Earth Sciences
Footwall-style Cu-Ni-PGE mineralization at the Sudbury Igneous Complex is hosted within extensive zones of brecciated footwall rocks. Our study, in collaboration with the multinational mining company Vale, sought to compare and contrast geochemical variations in Sudbury breccia adjacent to footwall ore zones to constrain the origin and extent of post-impact alteration surrounding the base metal mineralization and to identify geochemical vectors towards mineralized zones.
In O’Callaghan et al (in review)1 we utilized the electron microprobe at the Earth and Planetary Materials Analysis Laboratory to perform trace element analysis and high-resolution mapping of breccia matrix minerals at two active mines, focussing on biotites [K(Mg,Fe)3AlSi3O10(OH)2], titanites [CaTiOSiO4], chlorites [(Mg,Fe,Al)3(Si,Al)4O(OH)2] and Ca-Amphiboles [(Na,K)Ca2(Mg,Fe,Al)5(Si,Al)8O22(OH)2]. In particular the microprobe allows for precise analysis of trace metals and mobile elements such as chlorine and fluorine.
At Creighton Mine (South range) our study observed nickeliferous, chlorine-rich ferro-tschermakitic amphibole as rims on pre-existing actinolite grains that is indicative of multiple hydrothermal events under increasing pressure conditions (figure 1 and 2). Similarly, titanite exhibited geochemical variations that indicate increased temperatures towards post-impact, ore-hosting shear zones in the area. In contrast at Coleman Mine (North range) amphibole and biotites are replaced by Fe±Ni chlorites with proximity to mineralized zones. Geothermometry based on vacancies in the octahedral site of chlorite demonstrate a decreasing temperature gradient away from structures hosting sulfide mineralization, which are mirrored by decreasing trace-metal content (from 2.70wt.% to 0.03wt.% NiO) (figure 3). Our study concluded that although metal remobilization was spatially limited, certain trace elements may serve as vectoring tools towards structures hosting mineralization.
1 O’Callaghan J.W., Linnen R.L., Lightfoot P.C., Osinski G.R. 2016. Contrasting Mineralogical and Geochemical Charachteristics