Monazite as an Exploration Tool for Iron Oxide-Copper-Gold Mineralisation in the Gawler Craton, South Australia

Caroline Tiddy,Adrienne Brotodewo,David Giles,Jim Hodgkison,Mitchell Neumann,Diana Zivak,June Hill

doi:10.3390/min11080809

Abstract

The chemistry of hydrothermal monazite from the Carrapateena and Prominent Hill iron oxide-copper-gold (IOCG) deposits in the IOCG-rich Gawler Craton, South Australia, is used here to define geochemical criteria for IOCG exploration in the Gawler Craton as follows: Monazite associated with IOCG mineralisation: La + Ce > 63 wt% (where La > 22.5 wt% and Ce > 37 wt%), Y and/or Th < 1 wt% and Nd < 12.5 wt%; Intermediate composition monazite (between background and ore-related compositions): 45 wt% < La + Ce < 63 wt%, Y and/or Th < 1 wt%. Intermediate monazite compositions preserving Nd > 12.5 wt% are considered indicative of Carrapateena-style mineralisation; Background compositions: La + Ce < 45 wt% or Y or Th > 1 wt%. Mineralisation-related monazite compositions are recognised within monazite hosted within cover sequence materials that directly overly IOCG mineralisation at Carrapateena. Similar observations have been made at Prominent Hill. Recognition of these signatures within cover sequence materials demonstrates that the geochemical signatures can survive processes of weathering, erosion, transport and redeposition into younger cover sequence materials that overlie older, mineralised basement rocks. The monazite geochemical signatures therefore have the potential to be dispersed within the cover sequence, effectively increasing the geochemical footprint of mineralisation.

Highlights

We present trace and rare earth element geochemistry for monazite in the Carrapateena iron oxide-copper-gold (IOCG) deposit of the Gawler Craton, South Australia
Separation of monazite from basement rocks at Carrapateena into three geochemical groups is controlled by light REE (LREE), middle REE (MREE), Y and Th content (Figure 6)
Three compositional groups of Carrapateena basement data can be distinguished, confirming the results indicated in the element scatter plots, i.e., that Group 1 and 2 Carrapateena monazite have a distinct chemistry relative to background monazite compositions

Summary

Introduction

Heavy mineral phases preserved within sedimentary cover sequence materials that overlie mineralised basement rocks have been demonstrated to be useful in mineral exploration (e.g., [1,2,3,4,5]). The presence of heavy minerals in cover sequence materials may be used as an indicator for buried prospective basement rocks (e.g., [5,6,7]). The chemistry of heavy, resistate mineral phases may be used as an indicator for mineralisation. 1600−1590 Ma evolution of the Gawler Craton is marked by a major episode of IOCG mineralisation [9,10]. The challenge for explorers in the Gawler Craton is that it is overlain by extensive Neoproterozoic to Phanerozoic cover sequences [12,13].

Methods

Results

Discussion

Conclusion