Authored by Stacey Leichliter – Stacey has published numerous articles on geo-metallurgy, domestically and internationally. Stacey has served as an exploration geologist, working and performing research on epithermal gold and porphyry gold-copper deposits. She received her undergraduate degree in Geology at Missouri University of Science and Technology and her graduate degree in Geology (Geometallurgy) from the University of Tasmania/CODES (Australia).
Stacey Leichliter is a geo-metallurgist and has used near-infrared (NIR) instrumentation to characterize ore mineralogy at mine sites like AngloGold’s Cripple Creek facility in Colorado, USA. Upon demoing the ASD handheld TerraSpec® Halo mineral identifier, Stacey thought that the Halo was not only a valuable tool for the explorationist but also the Mine Geologist. Here are her notes on why the TerraSpec Halo is an important instrument for the Mine Geologist/Geometallurgist.
Abstract: Introduced late 2013, the TerraSpec Halo is a near-infrared (NIR) spectroscopy instrument developed by ASD, a Malvern Panalytical brand, available for the mining industry. Long used by exploration geologists to map alteration mineralogy, NIR is a popular tool in the mining sector although it has historically been a bulky but transportable apparatus that required a certain level of expertise to operate. The TerraSpec Halo was designed specifically for exploration geologists to be much more portable and easy to use in the field. Its lightweight design makes it applicable for mine geologists as well. NIR is used by mine geologists to help identify important and detrimental minerals, which can aid in determining how to separate the ore from the waste. The portability of the TerraSpec Halo allows the Mine Geologist to field identify valuable and problematic mineralogy in ores for stockpiling, extraction, and other tasks. This efficient ore control method reduces risk and provides the finest ores for processing, which reduces costs and increases profits.
Introduction and the TerraSpec Halo
The TerraSpec Halo is a rugged mineral identifier designed for the field geologist for quick analysis of rocks and minerals. This instrument is designed for mining exploration, but it can also be a critical tool for the active mining process as well. Mine geologists can use the equipment to efficiently classify waste, ore, and possible problematic ore, as its portability makes it easy to take to different parts of the mine or the ore feed to determine real-time mineralogy. The TerraSpec Halo allows for greater control during the ore control phase and can provide field validation for the metallurgical engineers during ore processing. By gaining this valuable information in real time, the plant has the ability to react if needed; thereby ensuring optimal ore recovery.
NIR has been providing important mineralogy information to geologists, engineers, and mine planners for decades. As ore grades decrease and ore mineralogy becomes increasingly important in order to maximize recovery, mineralogy information from NIR instruments helps with decisions in all aspects of the mining process: exploration, geotechnical, blasting, ore control, comminution (crushing and grinding), gravity/flotation, leaching, and environmental and sustainable issues. While NIR as a technology cannot detect all minerals as minerals such as sulfide group minerals and quartz do not reflect light well, NIR can differentiate important clay species and detect carbonates, oxides, phosphates, and sulfates. Any of these minerals can be important ore or formation indicator minerals or present problems for ore production. The TerraSpec Halo can take readings on cores, RC chips, blast chips, geologic and pit wall mapping, hand samples, outcrop/mine face and other sampling needs allowing for on-the-spot mineral identification.
The TerraSpec Halo is the next generation of (NIR) mineral identification instruments for the mining and geologic industry. Its portable design and extensive mineral library allow for many applications on the mine site and its ease of operation permits technician level data collection if desired. The handheld form factor of the TerraSpec Halo not only makes the technology more portable but automated procedures on Halo make it much easier for technician level personnel to operate with accuracy given appropriate supervision.
Applications of the TerraSpec Halo for the Mine Geologist
The mine geologist has many roles at the mine sites: mine mapping, ore delineation, infill drilling, and delivering production reports. They also provide ore control, minimize dilution, sort and track ore types for stockpile quality and quantity. Data produced by the mine geologist requires some resource modeling, assists in mine planning, and aids geotechnical engineers. These tasks are all vital to ensuring the proper and correct ore type and the amount is processed on a daily basis.
The TerraSpec Halo is the perfect instrument to aid the mine geologist in these tasks. Its ability to provide portable, real-time mineralogy with minimal or no sample preparation (the sample surface does need to be dry) makes it a valuable tool. Quick on-site mineral information helps the mine geologist to delineate the ore body and minimize dilution, as well as early notification of technical personnel and managers further down the mining flow sheet so any adjustments can be made. (i.e. crushing, grinding, gravity, flotation, leaching, and environmental).
Certain minerals detrimental in the extraction of the ore (i.e. clays, oxides, sulfates, phosphates, certain silicates) are identifiable with the TerraSpec Halo. These minerals depress or prevent the recovery of the ore unless certain chemicals or processes are provided. To prevent a decrease in recovery and loss of revenue, this information must be gathered prior to extraction. The perfect point to gain this information is during the mine mapping and ore control stages, as well as during the exploration stage.
Example TerraSpec Halo Scenarios for the Mine Geologist
Take a gold ore sample (Figure 1) and then quickly scan the sample with the TerraSpec Halo. It shows the following minerals found in the sample: montmorillonite, Mg-illite, Fe oxide, Fe oxyhydroxides, and jarosite. What implications do these minerals have on the mining and processing of this type of ore? Clay minerals cause problems in the geotechnical stability of the high walls, comminution (crush and grind), flotation, and even the leaching circuits. The oxides coat the ore and cause issues in the flotation and leaching circuits. Finally, Fe oxides, Fe oxyhydroxides, and jarosite cause leaching and pH fluctuations through the leach pad and waste dumps, which lead to leaching and environmental concerns.
A copper ore sample (Figure 2) that has a host rock of diorite shows a TerraSpec Halo mineralogy of Cu oxides, goethite, muscovite, chalcanthite, montmorillonite, and kaolinite. The oxides make leaching the preferred method of extraction. If flotation is used, the oxides, muscovite, chalcanthite, and clays cause problems. Clays cause problems in the slope stability and leaching. The Cu oxides cause pH fluctuations in the leach pad and waste.
A molybdenum ore (Figure 3) when scanned with the TerraSpec Halo shows anhydrite/gypsum, topaz, kaolinite, calcite, biotite, and muscovite. In this case, the clays, calcite, biotite, muscovite, and anhydrite/gypsum are problematic for the slope stability, comminution circuit, flotation, and leaching. The topaz is an abrasive mineral which wears on the comminution circuit equipment.
Finally, a sample of iron ore (Figure 4) scanned with the TerraSpec Halo may show the following minerals: actinolite, calcite, garnet, epidote, Fe oxides, kaolinite, and montmorillonite. What effects will these minerals have on the production of iron? The clays have the same issues with slope stability, comminution, flotation, and leaching. Actinolite and calcite have issues in the comminution and flotation circuits as well. Garnet and epidote are abrasive minerals, which wear down the comminution equipment.
These questions about the various types of ore samples are faced every day by mine geologists. Rapid response in the field is ideal. This is where the TerraSpec Halo is valuable as the immediate mineralogical information aids geologists, engineers and managers to be more proactive in mining operations increasing overall efficiencies, improving ore recovery and reducing costs.
A mine geologist can now easily determine real-time mineralogy using the TerraSpec Halo and know whether there are possible extraction issues with the ore. These potential problems exist in every stage of the mining process: geotechnical, planning, comminution, gravity/flotation, leaching, and environmental concerns. The portable design of the TerraSpec Halo enables it to be easily used in all parts of the mining operation. With the mineralogical data provided by the TerraSpec Halo, mine geologists have access to the real-time information vital to reducing costs and improving ore recovery and mining revenue.
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