Application of fractal analysis for quantitative assessment of critical mineral commodites (on example of Polokhivske lithium deposit)

• Published in: Мінеральні ресурси України no. 3; pp. 10 - 15
• Main Authors: O. I. Bilous, V. O. Parfeniuk, V. P. Bezvynnyi, B. I. Slobodian
• Format: Journal Article
• Language: English
• Published: Ukrainian Geological Company (UGC) 01.09.2024
• Subjects: economic evaluation; number-size fractal analysis; polokhivske deposit
• ISSN: 1682-721X; 2707-8698
• DOI: 10.31996/mru.2024.3.10-15

The characteristic feature of many deposits of critical raw materials is spatial chaotic fluctuations of grades (strongly skewed and lognormal distributions, soft geological boundaries etc.), which essentially limit the use of traditional economic evaluation methods and, especially, geostatistics. A possible solution may be application of various fractal methods based on the principle of multiple divisibility of geological object to the size of its elementary part, called fractal. Today fractal methods are widely used in life sciences, physics, mathematics, and chemistry, and are increasingly becoming used in biology and Earth sciences. For example, geological and mining for oil and gas apply fractal methods as a standard tool. A review of the literature in these areas shows that there are many issues in the field of critical raw materials that can be solved using fractal methods. Polokhivske deposit of LCT-type pegmatites with monomineralic fine-grained petalite ore was chosen for the case study. Pegmatites of Polokhivske deposit lack zoning and are characterised by uneven distribution of multi-grained mineral associations. Composition of pegmatites depends on the quantitative ratio of potassium feldspar, albite, and petalite. The difficulty to reveal any ore control features is explained by the proximity of the silica saturation and alkalinity of the hosting granites and fluids that transformed them. The moving average depth-grade method was used to solve specified issue. The clear trend of rhythmically increasing lithium content with depth was uncovered. This indicates that the deposit can be modelled as separate mineralised zones, each of which contains areas enriched with lithium and the location of such enriched areas must obey a certain regularity. This number-size fractal method was applied in order to separate potentially ore-bearing zones and mineralised geochemical anomalies of lithium from its background values. It has been proved the validity of this method to justify direction of exploration, economic evaluation, and mine planning. The resulting number-size model appeared powerful that revealed three mineralised zones within hosting granites: weakly mineralised metasomatically altered granites (0.08% ≤ Li₂O < 0.72%), mineralized metasomatites (0.72% ≤ Li₂O < 1.50%), and high-grade mineralised pegmatites (Li₂O ≥ 1.50%). The distinguished thresholds have appeared to be in sequence and multiple of the fractal dimension. From resulted model a spatial anisotropy of lithium grades was revealed: mineralised metasomatites spatially gravitate to the foot wall of weakly mineralised granites, and high-grade pegmatitic zones gravitate to the foot wall of mineralised metasomatites. Distribution of mineralised metasomatites and pegmatites shift northeasterly from the central axis of the Polokhivsky granitic massif.