Current Techniques and Applications of Mineral Chemistry to Mineral Exploration; Examples from Glaciated Terrain: A Review

This paper provides a summary of traditional, current, and developing exploration techniques using indicator minerals derived from glacial sediments, with a focus on Canadian case studies. The 0.25 to 2.0 mm fraction of heavy mineral concentrates (HMC) from surficial sediments is typically used for indicator mineral surveys, with the finer (0.25–0.50 mm) fraction used as the default grain size for heavy mineral concentrate studies due to the ease of concentration and separation and subsequent mineralogical identification. Similarly, commonly used indicator minerals (e.g., Kimberlite Indicator Minerals—KIMs) are well known because of ease of optical identification and their ability to survive glacial transport. Herein, we review the last 15 years of the rapidly growing application of Automated Mineralogy (e.g., MLA, QEMSCAN, TIMA, etc) to indicator mineral studies of several ore deposit types, including Ni-Cu-PGE, Volcanogenic Massive Sulfides, and a variety of porphyry systems and glacial sediments down ice of these deposits. These studies have expanded the indicator mineral species that can be applied to mineral exploration and decreased the size of the grains examined down to ~10 microns. Chemical and isotopic fertility indexes developed for bedrock can now be applied to indicator mineral grains in glacial sediments and these methods will influence the next generation of indicator mineral studies.

Typomorphic properties of kimberlite indicator minerals and their use in forecasting diamond deposits on the Siberian Platform

The results of mantle nodule investigations in kimberlite diatremes of the main Siberian Platform diamondiferous regions were analyzed. Morphology and chemistry of garnets, chrome-diopsides, clinopyroxenes, olivines, picro-ilmenites, chromites, chrome-spinellids and diamonds were investigated in detail. Generally, the quantity of diamond association minerals is proportional to diamond potential of a certain kimberlite variety for each type of kimberlite rocks composing pipes.

Method of complex analyses of the compositions of kimberlite indicator minerals to assess the presence of large diamonds

<p>For industrial deposits that contain particularly large and expensive diamonds, a diagram of the compositions of KIM (kimberlite indicator minerals) for Cr, Al, Fe, Mg, Mn is proposed. The proximity or rather convergence of the compositions of KIM is also complemented by a high correlation of the frequency of occurrence of their cluster groups (Ivanov, 2017), such as pyropes, chromites, picroilmenites and pyroxenes. The increase in oxygen fugacity  in  KIM is correlating with Fe and Ti , this fact can also explain the intensity of metasomatism of kimberlites, shown in the proposed graph by an increase in ilmenite content. This type of diagram was proposed by Mitchell (1986) for chromite compositions, which the authors supplemented with compositions of  picroilmenites, pyropes and pyroxenes. The manganese  concentration is shown by the size of the figurative point  – a bubble diagram. For better perception, the drawing is supplemented with different colors of the composition groups of  KIM. Below are diagrams for two industrial deposits that contain expensive and large diamonds. The diagrams show the approximate regions of diamond-bearing associations for chromite and pyrope compositions with red asterisks. The blue lines show two main trends in chromite compositions, the horizontal one is picrate trend and the vertical one is kimberlite. For picroilmenite compositions, the diagram shows two main trend lines: the red line for paramagnetic compositions and the black line for ferrimagnetic compositions. For pyrope compositions, trend lines are shown in red for a number of cluster groups G10 by (Dawson, Stephens, 1975) and for groups G11 – in black. The diamond content in kimberlites of the Aykhal pipe is several times higher than in the Komsomolskaya pipe, but the cost of diamond crystals from the latter is several times more expensive than in the Aykhal pipe. A distinctive feature of the compositions of the Komsomolskaya pipe KIM, as well as the above-proposed kimberlite pipes (Griba and Karowe ) – is the presence of diamond-bearing websterite parageneses of chromites and pyropes, which corresponding in the diagram, to areas with elevated Cr, Fe  values . The kimberlite of the Aykhal pipe is characterized by a higher degree of metasomatism, which is recorded in the diagram by the trend of more ferruginous picroilmenite compositions, which affects the quality of its diamonds.</p><p>CONCLUSIONS. The proposed method is based on a comprehensive assessment of KIM compositions. The diagram allows to assess the presence of expensive and large diamonds in kimberlite pipes at the  exploration  stage, as well as to reconstruct the composition of deep mantle rocks, based on  the KIM graphically presenting analyses of their compositions for five elements.</p><p>1. Ivanov A. S. Statistical analysis of indicator minerals of kimberlites. Proceedings of the XIII All-Russian (with international participation) Fersman session. KSC RAS. G. Apatity. 2017. C. 172-181.</p><p>2. Mitchell R.H. Kimberlites: mineralogy, geochemistry and petrology. New York, Plenum Press. 1986. 442 P.</p><p>3. Dawson J.B., Stephens W.E. Statistical classification of garnets from kimberlites and xenoliths. J. Geol. 1975. 83, 589-607.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.e9220f156dff55102440161/sdaolpUECMynit/12UGE&app=m&a=0&c=0f83753a5548fc75c9d09360ceb8fba7&ct=x&pn=gepj.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.d0e4b6356dff58302440161/sdaolpUECMynit/12UGE&app=m&a=0&c=8ee1cd160278a2b43eaa34c7046345f5&ct=x&pn=gepj.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.5103f8a56dff52512440161/sdaolpUECMynit/12UGE&app=m&a=0&c=597c719fd1593d0deb555868e8cf03aa&ct=x&pn=gepj.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.241bc3c56dff59712440161/sdaolpUECMynit/12UGE&app=m&a=0&c=4dccd20a38e5bad392e02c82cfe84981&ct=x&pn=gepj.elif&d=1" alt=""></p><p> </p><p> </p>

Chemical studies of kimberlite indicator minerals from stream sediment and till samples in the southern Mackenzie region (NTS 85B, C, F, G), Northwest Territories, Canada

Till (n=196) and stream sediment (n=60) samples were collected in the area south and west of Great Slave Lake, Northwest Territories (NTS 85B, C, F, and G), over the course of 3 summer field seasons. Samples were processed to recover kimberlite and other indicator minerals. This report summarizes results of the kimberlite indicator mineral (KIM) studies, including measures of KIM mineral types, abundances, and chemistry (major, trace, and rare earth elements). KIMs were present in 24% of the samples collected, and only 183 KIM grains in total were recovered, of which Cr-pyrope garnets were the most abundant (65.6%). Chemical analyses revealed strong similarities to the Drybones Bay and Mud Lake kimberlites which are situated 50 to >100 km to the northeast, roughly aligned with prominent glacially streamlined landform flowsets in this field area. Results suggest there is little evidence for undetected kimberlite outcrop or sub-crop in the study area.

The new Massadou diamondiferous kimberlite field in Guinea

A new kimberlite field, called Massadou, has been discovered in southeastern Guinea near Macenta city. The field consists of numerous ~1 m thick kimberlite dikes with low diamond contents; altogether 16 dikes have been found so far. Mineralization occurs along a 600 m wide zone distinct in satellite images, which is oriented in the same way as the K4 kimberlite reported by Huggerty. The Massadou kimberlite is covered by a thick laterite weathering profile. Main kimberlite indicator minerals found in the area are pyrope, chromite, and ilmenite. The latter occurs as zoned grains with a high-Fe core (hemoilmenite) surrounded by a parallel-columnar aggregate in the rim. The aggregate has a composition of ordinary kimberlitic Mg ilmenite and results from interaction of hemoilmenite with the kimberlite melt. The kimberlite age is estimated as 140—145 Ma by analogy with the surrounding fields. The dikes independent products of kimberlite magmatism in the Guinea-Liberia shield rather than being roots of pipes as interpreted by Skinner (2004). Therefore, the erosion cutout is moderate, and there are no reasons to expect the presence of large and rich diamond placers.