The Influence of Thermal Differences and Variation of Cl–F–OH Ratios on Cu-Ni-PGE Mineralization in the Contact Aureole of the South Kawishiwi Intrusion, Duluth Complex

Zsolt Benkó,Steven Hauck,Ferenc Molnár,Karl Ettinger,Mark Severson,Aberra Mogessie

doi:10.3390/geosciences8120474

Abstract

In the contact metamorphic aureole of the Duluth Complex, Cu-Ni-PGE mineralization occurs locally up to 100 m from the intrusion-footwall contact (Spruce Road area), whereas elsewhere (Dunka Pit deposit) the footwall granite and metapelite (Serpentine deposit) are barren. This study aimed to understand the effect of temperature and halogen fugacity variations on the presence or absence of mineralization in these footwall units. The mafic mineral assemblages, two-pyroxene, titanium-in-quartz, and biotite-apatite thermometers indicate that temperatures could be as high as 920 °C in the mineralized areas of the footwall, whereas the maximum temperature was lower by about 100 °C in the unmineralized part of the intrusion. Variation of the halogen concentrations and fugacities was monitored with the analysis of halogen concentrations in biotite and apatite. Fluorine and chlorine concentrations in biotite increase as a function of the distance from contact in the mineralized drill core and decrease in the unmineralized zones. Chlorine concentrations in apatite increase parallel with the distance from contact in the mineralized zones, whereas fluorine concentrations show only minor variation. Concentrations of these elements may have had subtle effect on the partial melting in the footwall units and indirectly facilitated the infiltration of the sulfide liquid into the footwall.

Highlights

Interaction between voluminous mafic intrusions with country rocks results in the formation of thick contact metamorphic zones, such as in Bushveld Complex, South Africa; Portimo Complex, Finland; and East Bull Lake Intrusive Suite, Canada [1,2]
The mineralization of footwall/country rock is commonly enriched in Cu and PGE when compared to the mafic intrusion [1,2] and may form economically significant, exploitable orebodies (e.g., McCreedy West, McCreedy East, Broken Hammer deposits in the footwall of the Sudbury Igneous Complex [3,4,5]; Sandsloot mine, Platreef, Bushveld [11])
In the contact-metamorphosed granitic footwall of the South Kawishiwi intrusion, Duluth Complex, a Cu-Ni-PGE-Au mineralization (0.5% Cu and 900 ppb Pt + Pd + Au) at the Spruce Road area has been reported in the 90s [12,13]

Summary

Introduction

Interaction between voluminous mafic intrusions with country rocks results in the formation of thick contact metamorphic zones, such as in Bushveld Complex, South Africa; Portimo Complex, Finland; and East Bull Lake Intrusive Suite, Canada [1,2]. The interaction may generate partial melting and circulation of hydrothermal fluid flow in the footwall of large igneous complexes, as seen in Sudbury Igneous Complex [3,4,5,6,7], and injection and assimilation of partial melts and volatiles from the footwall rocks [8,9,10]. These processes influence the transport and crystallization of base and precious metals, and the formation of Cu-Ni-PGE sulfide deposits in the contact. Partial melting of the footwall up to 125 m from the intrusion–footwall contact was documented at the Spruce Road deposit [16,20,21,22] and showed that partial melting played a significant role in the filtration of the sulfide liquid downward into the footwall of the intrusion

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Results

Discussion

Conclusion