Geoscience and Exploration

New Trends in Gold Mineralization Investigated at the Yellowknife City Gold Project Using Synchrotron X-ray Spectroscopy

Soapbox Wednesday, November 21, 2018 - 13:00 to 13:06 Theatre 2


R.J. Botor (Presenting)
Western University

H.E. Cavallin
Western University

T.J. Flynn
Western University

A. Sexton
TerraX Minerals, Inc.

J. Campbell
TerraX Minerals, Inc.

L.L. Van Loon
LISA CAN Analytical Solutions

N.R. Banerjee
Western University

The Yellowknife City Gold Project (YCGP) encompasses 780 km2 of contiguous land north, south and east of the city of Yellowknife. It lies in the prolific Archean north-south trending Yellowknife Greenstone Belt, a suite of mafic and felsic volcanics, and greywacke turbidites overlying a gneissic basement. Host rock alteration include chloritization, sericitization, and carbonatization, plus biotite alteration in wall rock. TerraX Minerals Inc. focuses its exploration and drilling efforts along 70 km of strike length on the southern and northern extensions of the mineralized shear zones and quartz veins associated with the past-producing, high-grade Con (6.1 Moz @ 16.1 g/t Au) and Giant (8.1 Moz @ 16.0 g/t Au) gold mines. Gold grades in core and surface rock samples related to this study range from 0.1-~200 g/t, with higher gold grades associated with mafic volcanic and greywacke hosts. Gold is associated with quartz veins and disseminated sulphides, including pyrite-arsenopyrite or sphalerite-galena in As-poor mineralization, and within sericite-chlorite.

Synchrotron analyses applied to mineral exploration can address industry-relevant questions and provide rapid solutions that add significant value using innovative, high-resolution analytical techniques. Synchrotron X-ray fluorescence (SR-XRF) spectroscopy is a nondestructive technique providing in-situ trace element analysis for ore mineral mapping and zonation. X-ray absorption near edge structure (XANES) spectroscopy can determine speciation of gold, arsenic and other trace elements, useful for geometallurgy and deleterious element characterization. Synchrotron X-ray diffraction (SR-XRD) is a rapid technique for mineralogical analysis, providing critical mineralogical information on altered and mineralized samples. Such methods can be performed on many types of materials without specialized sample preparation. We have developed novel, non-destructive SR-XRF techniques that can be performed directly on half-core samples or surface sample slabs and produce trace element maps >10 cm long by up to 5 cm wide. The technique provides critical trace-element associations in gold-bearing sulphide minerals that provide integral information regarding the nature of mineralizing fluids.

Synchrotron X-ray diffraction of 71 powdered samples, and X-ray fluorescence maps of 73 slabs and half cores reveal similarities in mineralization styles between the Northbelt Property (i.e., Sam Otto, Crestaurum, Barney, Mispickel, and Homer Lake Zones) and the Con-Giant Mines, such as early pyrite-arsenopyrite mineralization overprinted by later sericite, quartz-carbonate, and sphalerite-galena, hinting that both locations are likely derived from a single mineralizing system. Our results suggest the timing of mineralization is similar throughout the Yellowknife City Gold Project. Overprinting relationships confirm findings from earlier studies that propose high-As sulphides formed first, followed by sericite-quartz-carbonate-chlorite alteration assemblages, and later low-As sulphides. The Yellowknife River Fault Zone and its splays likely act as conduits for fluid percolation and mineralization during metamorphism. Three main gold associations are present across the YCGP – gold+sulphide, gold+quartz-carbonate, and sericite-hosted gold, with the two latter due to later remobilization during syn-mineralization metamorphic processes. XANES analyses of samples where gold was identified by SR-XRF reveal the presence of only metallic Au within sulphides and quartz veins. No refractory gold associated with elevated arsenic levels has been observed suggesting gold may be easier to recover than previously thought.