A Holistic Approach to Mineral Exploration
Mineral Systems Approach (MSA) is an exploration targeting practice that has been gaining momentum in the mineral exploration community as the modern, holistic method of identifying new, potentially major mineralisation districts.
A Mineral Systems Approach has been, at least in part, involved in the discovery of world-class mineral deposits, such as Olympic Dam, Yeelirrie, Cannington, and Gruyere. MSA is part of the exploration toolbox being used for regional exploration targeting by SRK Exploration Services Ltd (SRK ES), major mining companies, and academic institutes.
Using a Mineral Systems Approach, an exploration geologist considers the large-scale geological systems and processes over geological time and applies these to ore formation processes. Using regional datasets in GIS software, the geologist searches for characteristic markers for metal-ion fertility, fluid transport architecture, and physical/chemical trap-sites, whilst considering the near-surface preservation of any potential deposit. The approach is used to highlight new regions of potential mineralisation which may have no geochemical or structurally anomalous features at surface and/or were overlooked historically due to various reasons. The approach considers ore deposits as fossilised remnants of much larger earth process systems which focus mass and energy movement at specific times in the Earth’s development. The best way to predict the location or metal endowment of these fossils is to understand the geological system of the area of interest in its entirety and at a variety of scales.
Development of Mineral Systems Approach has been enabled through improved understanding of lithospheric crustal processes, optimisation of computing power and GIS software, and advances in regional geophysical techniques, digitisation of geological maps and the consolidation of large mineral occurrence datasets. These factors when brought together with sound geological theory and a healthy dose of “out of the box” thinking, permit geologists to revisit historical interpretations of ore genesis and where deposits form.
Applying the Concept
So how is the Mineral System Approach put into practice? SRK Exploration geologists have been working with world-renowned geologist and advocate of MSA, Jon Hronsky, to develop a procedure which can be used to systematically practice it in a consulting environment. The team was set the task of applying Mineral Systems Approach to target potentially prospective districts for orogenic gold and VMS mineralisation across Neoproterozoic terrains with the aim of developing a reproducible method which could be applied to any region globally.
The Approach utilises geological, geophysical, lithochemical, and geochronological data, where available, but is not wholly constrained by the presence or absence of data.
To maximise the targeting potential of MSA, a geologist would ideally have access to the following data:
public access satellite imagery;
- digitised geological mapping at least at a 1:500k scale;
- geo-referenced academic interpretive maps and figure
- high quality regional electromagnetic and radiometric data;
- high quality regional gravity data;
- geochronological data; and
- mineral occurrence data.
The methodology can be broken down into the following stages, though it should be emphasised that the process is an iterative one, which requires re-interpretation and evaluation when new or updated data becomes available.
1. Data processing - Interrogate each dataset to assess its use and adjust to optimise its efficacy.
Thoroughly review all relevant academic literature related to the region of interest to provide a foundation on which to base any interpretations.
- Geological maps vectorised in GIS software into polygons, with lithology and age information recorded as metadata.
- Geophysical data reprocessed to improve resolution and remove noise.
- Geochronological data classified by source, technique and confidence, then grouped by geological unit and age via population analysis.
- Maps and figures from academic papers georeferenced to be used as GIS layers to test and compare interpretations.
- Mineral occurrence data organised by mineralisation and commodity type, then ranked by size/importance.
Once these data are optimised, the data should be loaded as layers into adaptable GIS software.
2. Lithospheric Architecture Interpretation - The geological mapping data should be amalgamated and simplified based on lithological groupings, such as ultramafic units, felsic volcanics, greenstone belt-related units, exhumed basement, sedimentary basins, and younger intrusive and extrusive volcanics.
3. Structural Interpretation - Identify and digitise major structural features using satellite imagery, geophysical data and mapping, noting major inversions shown by gravity data and anomalies in geographical features such as changes in river orientation, termination of spreading centres and basins. It is possible to delineate structures underlying young extrusive rocks by digitising such features as linear clusters of volcanic vents or geophysical contrasts. The principal aim is to identify mantle-tapping structures which can focus mineral-carrying fluids from metallurgically fertile rock at depth. It is important to be cognisant that older structures are often reactivated by later tectonic events and that major, lithospheric scale structures may be masked by younger features.
4. Terrane Modelling - Using the structural and lithological interpretations, identify large-scale lithospheric architectural features such as rift zones, belt-scale antiformal structures and dome complexes, representing potentially fertile terranes. This process can be supported by geochronological data and academic interpretive figures, against which interpretations can be cross-examined. Geophysical data can often be used to extrapolate lithological and structural interpretation beyond where mapping data wasn’t available, or where terranes were unconformably underlain beneath younger units.
5. Prospective District interpretation - With the potentially mineralised terranes identified, the next step is to use more refined data along with a mineral occurrence database to delineate prospective district or camp-scale areas along favourable lithologies, unit boundaries and/or structures.
6. Identification of new/under-explored Search Spaces - These are geographical areas which for various reasons have been under-explored/ignored by exploration teams in the past. This may be due to the nature of the target ore-type, overlying younger cover, available detection technology at the time and the prevailing political/commercial environment (including factors such as tax regimes, metal prices and available infrastructure). SRK ES will then delineate areas which were identified as potentially prospective but had been overlooked in the past due to overlying sedimentary basins, aeolian sands or extrusive rocks. These are ranked in order of prospectivity and used as a basis for further exploration.
7. Deposit Scale Assessments – Based on technical site visits or assessments of specific targets, deposit scale inferences are brought into the overarching model. These are used to identify mappable targeting criteria that reflect fundamental critical processes in the mineral Systems model and enable future exploration programmes to better target new discoveries.
By using and refining each stage of this methodology, SRK ES has been able to develop a procedural approach for which to apply the Mineral Systems Approach concept. A complementary step to this process would be to supplement the model with a mathematical knowledge or data driven prospectivity analysis. This process would leverage the critical targeting criteria identified using Mineral Systems Approach as vectors to be used part of a machine learning exercise. The results of which could be used to test exploration concepts and potentially highlight new search spaces.
Providing the Mineral Systems Approach to the World
To conclude, SRK ES with the support of Mineral Systems Approach experts, have developed a Mineral Systems procedural framework based on decades of exploration experience, comprehensive geological understanding, in-depth knowledge of cutting-edge software and data acquisition. With the appropriate data and collaboration, SRK ES is assisting explorers around the world using the Mineral Systems Approach to discover the tier-one deposits of the future.
