Mineralogy, geochemistry, and genesis of the Chahgaz (XIVA Anomaly) Kiruna-type iron oxide-apatite (IOA) deposit, Bafq district, Central Iran
9
Citation
80
Reference
10
Related Paper
Citation Trend
Keywords:
Felsic
Metasomatism
Ore genesis
Diorite
Tourmaline
Metasomatism
Pegmatite
Protolith
Cite
Citations (1)
The Central Mineral Belt (CMB) in Labrador, Canada, hosts multiple U (±base ± precious metal) showings, prospects and deposits in metamorphosed and variably hydrothermally altered Neoarchean to Mesoproterozoic, igneous and sedimentary rocks. Previous work has recognized U mineralization locally associated with Fe-Ca and alkali metasomatism typical of metasomatic iron oxide and alkali-calcic alteration systems (IOAA) that host iron oxide-copper-gold (IOCG) and affiliated critical metal deposits. However, the type, extent and temporal or genetic relationships between the diverse Fe, Ca and alkali metasomatism and the regionally distributed U mineralization remains poorly understood. Combined unsupervised machine-learning and classification of alteration from a large geochemical dataset distinguish the main alteration phases in the CMB, identify compositional changes related to U mineralization, and infer lithological/mineralogical information from samples with censored (i.e., missing), limited and/or inaccurate metadata. Weak to intense Na and Na + Ca-Fe (Mg) metasomatism in the southwest (Two-Time and Moran Lake areas) and eastern (Michelin area) portions of the CMB pre-dates U mineralization and Fe-oxide breccia development, similar to albitite-hosted U and IOCG deposits globally. Rare earth elements and spider diagrams highlight both preservation and disruption of normally immobile elements. Principal component and cluster analysis indicate significant variations in Fe-Mg ± Na contents in the rocks from combinations of Na, Ca, Fe, and Mg-rich alteration, while protolith REE signatures can be locally preserved even after pervasive albitization-hematization. Cluster analysis identifies mineralized felsic and mafic rocks in the Michelin deposit and Moran Lake area, facilitating inference of relevant lithological/mineralogical information from samples lacking or with limited meta-data. The methods outlined provide rapid and relatively inexpensive means to optimize identification of mineral systems within large geochemical datasets, verify drill core or field observations, highlight potentially overlooked alteration, and refine economic mineral potential assessments. Based on our results and previous work, we suggest the mineral potential of the southwestern and eastern CMB needs to be re-assessed with modern exploration models for IOAA ore systems and their iron oxide-poor variants.
Metasomatism
Felsic
Cite
Citations (5)
Felsic
Caldera
Cite
Citations (0)
Felsic
Lineation
Diorite
Magma chamber
Cite
Citations (31)
Metallogeny
Ore genesis
Protolith
genetic model
Breccia
Cite
Citations (9)
Iron oxide copper gold (IOCG) deposits are globally important sources of Cu; however, their origins remain poorly understood with respect to the metal and fluid sources involved in their formation. In this work, we utilize integrated Fe, Ti, and O isotopic data for magnetite to trace major metal and fluid inputs for the Proterozoic-aged Ernest Henry IOCG deposit—the largest known IOCG deposit in the Cloncurry District, Queensland, Australia. Magnetite separates from ore stage and pre-ore biotite-magnetite (bt-mgt) and magnetite-actinolite (mgt-act) alteration assemblages from Ernest Henry were analyzed for their O, Fe, and Ti isotope abundances, reported as δ18O (VSMOW), δ56Fe (IRMM-14), and δ49Ti (OL-Ti). Select magnetite samples were also analyzed for 17O (reported as Δ'17O0.5305) and range from −0.118 to −0.056 ‰—suggesting evaporitic input. The δ18O values from ore stage (+1.57 to +7.36 ‰), bt-mgt (+0.34 to +5.68 ‰), and mgt-act (+1.68 to +2.10 ‰) samples are consistent with a magmatic-hydrothermal origin for ore and pre-ore mineralizing fluids at Ernest Henry; non-magmatic δ18O values > c. 5 ‰ may be explained through localized carbonate wall rock assimilation. Despite this, δ56Fe values for ore stage (−0.50 to +0.33 ‰), bt-mgt (−0.65 to +0.38 ‰), and mgt-act (−0.26 to +0.30 ‰) magnetite are generally isotopically lighter than the accepted range (c. +0.06 to +0.49 ‰) for igneous and magmatic-hydrothermal magnetite and exhibit a relatively large range of c. 1 ‰, suggesting Fe source mixing within the deposit. Ore stage magnetite δ49Ti (−1.64 to + 3.79 ‰; avg: +1.49 ‰; 2σ = 2.63 ‰) compositions are generally higher and more variable than either the bt-mgt (-0.44 to + 1.49 ‰; avg: +0.62 ‰; 2σ = 1.13 ‰) or mgt-act (+0.27 to + 1.89 ‰; avg: +1.05 ‰; 2σ = 1.56 ‰) and suggest that Ti isotope fractionation occurred due to differential mobility in the fluid. The data are best explained by models invoking both magmatic and non-magmatic metal and fluid input. Fluid flow channeled between the footwall and hanging wall shear zones introduced non-magmatic Fe that may have been leached from local mafic units by magmatic-hydrothermal fluids, resulting in neoformed and regeneratively replaced magnetite with magmatic δ18O, but non-magmatic δ56Fe values during pre-ore alteration. These fluids may have mixed with Fe-poor evaporitic fluids prior to magnetite formation. Later magmatic Fe and O contributions during ore stage mineralization resulted in magnetite with variable δ56Fe and irresolvable δ18O overprinting. Ernest Henry is the first known example of an IOCG deposit with a major leached metal component identified through metal stable isotope geochemistry.
Ore genesis
Cite
Citations (8)
The origin of Fe oxide-(Cu-Au) deposits and the relative role of played by magmas (both felsic and mafic) versus evaporite-rich country rocks as a source of fluids and/or metals remains controversial. A popular model for the formation of IOCG deposits in the Mt Isa Eastern Succession involves fluids derived from the late orogenic granites mixing with a second external fluid source forming Fe(commonly magnetite-) rich alteration zones that contain vein stockwork, breccia, dissemination or replacement style mineralization (Oliver et al., 2000). This is assumed to be commonly spatially and temporally associated with felsic pluton emplacement and cooling around 1540-1500 Ma. This contrasts with an alternative model in which the fluids are entirely intra-basinal and amagmatic in origin (Barton and Johnson, 1996). Recent dating studies at Osborne have highlighted a potential syn-peak metamorphic timing to mineralization (based on 1595 Ma Re-Os age dates on molybdenite and a 1595 ± 6 Ma U-Pb age date on hydrothermal titanite), with no apparent proximal major intrusion (Gauthier et al., 2001). There is also a potential link between mineralization and widespread mafic intrusive activity that occurs in the Eastern Succession for the entire range of known mineralization ages. Futhermore, at some deposits (276 orebody at Starra) intra-ore mafic intrusives have been recorded.
Felsic
Stockwork
Breccia
Cite
Citations (0)