Uranium-bearing hematite from the Olympic Dam Cu–U–Au deposit, South Australia: A geochemical tracer and reconnaissance Pb–Pb geochronometer

Rare Earth Element Behaviour in Apatite from the Olympic Dam Cu–U–Au–Ag Deposit, South Australia

“…Total acquisition time was 60 s for each analysis comprising a 30 s background measurement, 30 s of ablation and a 40 s delay between analysis allowing for adequate wash-out, gas stabilization and processing time. The following isotopes were analysed 23 Na, 24 Mg, 27 Al, 28 Si, 31 P, 34 S, 39 K, 43 Ca, 45 Sc, 47 Ti, 51 V, 55 Mn, 56 Fe, 57 Fe, 59 Co, 60 Ni, 63 Cu, 66 Zn, 75 As, 85 Rb, 88 The analyses of reference materials were performed after every ten sample analyses and comprised readings identical in every respect to that of the samples. Two analyses of NIST 612, followed by one of NIST 610 and a final two NIST 612 analyses comprised the standard run.…”

“…The samples investigated are the same as those described in [20], with the addition of one sample (three polished blocks) from massive bornite ore from the underground mine previously used for the U-Pb dating of hematite and zircon [31]. Overall, the sample suite encompasses Hiltaba-aged intrusive rocks (both felsic and mafic) displaying variable degrees of alteration, early magnetite-dominant mineralization (DM and DS), and high-grade bornite ore (Table 1, Figure 1).…”

“…Hematite occurs as two generations defined by textures and trace element signatures [45]. These are: (i) coarser, brecciated, porous and rounded grains poor in U-W-Mo, hosting discrete inclusions of REY-and U-minerals; and (ii) acicular aggregates with U-W-Mo-oscillatory zonation patterns; the latter was dated at 1577 ± 5 Ma [31]. Based on textures and trace elements patterns, the acicular hematite is younger than type (i), and hematite type (ii) is co-genetic with the studied apatite because it is observed to grow within it (Figure 6b,c).…”

“…In addition, fragments of milled hematite-(i) and bornite are found within apatite, which has undergone crystallization (developing crystal faces) as it seals brecciation within the bornite-hematite assemblage (Figure 6d). The massive bornite samples show multiple stages of overprint, including metamictization of zircon with recrystallized domains that were dated at 1343 ± 47 Ma [31] and surrounded by haloes of xenotime (Figure 6a, inset). Furthermore, the overprint is illustrated by the presence of a variety of trace minerals tied to fractures within hematite and grain boundaries, such as common florencite, a few µm in size, or rare interstitial U-bearing minerals (fine-grained coffinite-brannerite intergrowths), dusty inclusions of U and REY-bearing phases within altered hematite, as well as tiny flakes of molybdenite in bornite.…”

“…Lamellar chalcopyrite exsolutions occur in bornite adjacent to xenotime and rare, µm-sized chalcocite forms within fractured hematite of generation (i). Florencite contains nanometre-sized inclusions of hematite [31]. In addition, fractures containing milled, dusty fragments of all minerals in the assemblage are also present.…”