Trace element composition of iron oxides from IOCG and IOA deposits: relationship to hydrothermal alteration and deposit subtypes

Abstract

Trace element compositions of magnetite and hematite from sixteen well-studied iron oxide-copper-gold (IOCG) and iron oxide apatite (IOA) deposits, combined with partial least squares-discriminant analysis (PLS-DA), were used to investigate the factors controlling the iron oxide chemistry and the links between the chemical composition of iron oxides and hydrothermal processes, as divided by alteration types and IOCG and IOA deposit subtypes. Chemical compositions of iron oxides are controlled by oxygen fugacity, temperature, co-precipitating sulfides, and host rocks. Iron oxides from hematite IOCG deposits show relatively high Nb, Cu, Mo, W, and Sn contents, and can be discriminated from those from magnetite + hematite and magnetite IOA deposits. Magnetite IOCG deposits show a compositional diversity and overlap with the three other types, which may be due to the incremental development of high-temperature CaFe and K-Fe alteration. Iron oxides from the high-temperature CaFe alteration can be discriminated from those from high-and low-temperature K-Fe alteration by higher Mg and V contents. Iron oxides from low-temperature K-Fe alteration can be discriminated from those from high-temperature K-Fe alteration by higher Si, Ca, Zr, W, Nb, and Mo contents. Iron oxides from IOA deposits can be discriminated from those from IOCG deposits by higher Mg, Ti, V, Pb, and Sc contents. The composition of IOCG and IOA iron oxides can be discriminated from those from porphyry Cu, Ni-Cu, and volcanogenic massive sulfide deposits.

The Evolution of Metasomatic Uranium Ore Systems in the Central Mineral Belt of Labrador

“…low Sn (up to 10 ppm), possibly reflective of a high temperature, reduced fluid (Carew, 2004;Righter et al, 2006;Huang et al, 2019). Both the geochemical characteristics described and the nature of uraninite mineralization in sample 18-CD-10 which overgrows primary magnetite, could further support the interpretation of section 2.5.3…”

“…Trace element patterns of both samples overlap with the IOCG field as defined by Huang et al (2019) with the exception of vanadium (Fig. 3-3b).…”

“…This slightly contradicts the hydrothermal origin defined by the Ni/Cr ratios (Dare et al, 2014). Differences in V and Sn contents of IOAA-type magnetite have been interpreted to reflect differences in fluid temperature and oxygen fugacity, where an increase in oxidation and a decrease in temperature of the hydrothermal fluid can lead to a decrease in V and an increase in Sn contents of magnetite (Carew, 2004;Righter et al, 2006;Huang et al, 2019).…”

“…............................................................. 31 (Rudnick and Gao, 2003). Average trace element data for magnetite of high temperature hydrothermal deposits (high t htm), the Bushveld deposit (Fe-Ti-P type) and Banded Iron Formation deposit (Dare et al, 2014) and IOCG-type deposits (in green) (Huang et al, 2019) are also plotted.…”

“…-2: Minor to trace element box (in ppm) and whisker plot of magnetite from this study plotted alongside representative IOAA data fromHuang et al (2019).…”