Баянголын баруун VI төмрийн ордын интрузив чулуулгийн геохими ба геохронологи

Abstract

The Bayangol West VI iron deposit in northern Mongolia represents a multi-stage mineralization system genetically associated with dioritic magmatism developed in a subduction-related geodynamic setting. Petrographic observations indicate that the host rocks are predominantly composed of amphibole–plagioclase diorite with porphyritic textures, locally affected by metasomatic and hydrothermal alterations.

Geochemically, the rocks are characterized by low SiO₂ (42.45–46.99 wt%) and relatively high MgO (7.12–8.11 wt%) and CaO (10.43–14.01 wt%), with Na₂O/K₂O ratios of 1.22–2.09, indicating a calc-alkaline affinity typical of arc-related magmatism. Chondrite-normalized REE patterns show enrichment in light rare earth elements (LREE) with weak negative Eu anomalies, suggesting fractional crystallization. Primitive mantle-normalized trace element patterns display enrichment in large-ion lithophile elements (LILE) and depletion in high field strength elements (HFSE), consistent with subduction-related magma signatures. However, similarities to OIB-type patterns imply contributions from a relatively deep mantle source.

Zircon U–Pb geochronology constrains the timing of magmatism. Cathodoluminescence images reveal euhedral to subhedral zircons (50–300 μm) with well-developed oscillatory zoning, indicative of magmatic origin, supported by Th/U ratios of 0.17– 1.30. Weighted mean U–Pb ages from concordant analyses (n = 29) yield 439 ± 2 Ma (MSWD = 1.3), corresponding to crystallization during the Middle Ordovician to Early Silurian.

Integrated petrographic, geochemical, and geochronological results indicate that the mineralization formed in an island arc to continental arc transitional setting related to Paleozoic subduction. The iron mineralization is interpreted as a skarn-type system formed through multi-stage processes involving magmatic intrusion, contact metasomatism, structural control and subsequent hydrothermal overprinting.