Minor and trace elements can substitute into the crystal lattice of galena at various concentrations. In situ LA-ICP-MS analysis and trace element mapping of a range of galena specimens from ...different deposit types are used to obtain minor/trace element data, aimed at achieving insight into factors that control minor/trace element partitioning. The previously recognized coupled substitution Ag++(Bi,Sb)3+ ⇌ 2Pb2+ is confirmed. However, the poorer correlation between Ag and (Bi+Sb) when the latter elements are present at high concentrations (∼>2000 ppm), suggests that site vacancies may come into play: 2(Bi,Sb)3++∎ ⇌ 3Pb2+. Galena is the primary host of Tl in all mapped mineral assemblages. Along with Cu, Tl is likely incorporated into galena via the coupled substitution: (Ag,Cu,Tl)++(Bi,Sb)3+ ⇌ 2Pb2+. Tin can reach significant concentrations in galena (>500 ppm). Cd and minor Hg can be incorporated into galena; the simple isovalent substitution (Cd,Hg)2+ ⇌ Pb2+ is inferred. This paper shows for the first time, oscillatory and sector compositional zoning of minor/trace elements (Ag, Sb, Bi, Se, Te, Tl) in galena from two epithermal ores. Zoning is attributed to slow crystal growth into open spaces within the vein at relatively low temperatures.The present data show that galena can host a broader range of elements than previously recognized. For many measured elements, the data sets generated display predictable partitioning patterns between galena and coexisting minerals, which may be dependent on temperature or other factors. Trace element concentrations in galena and their grain-scale distributions may also have potential in the identification of spatial and/or temporal trends within individual metallogenic belts, and as markers of ore formation processes in deposits that have undergone superimposed metamorphism and deformation. Galena trace element geochemistry may also display potential to be used as a trace/minor element vector approach in mineral exploration, notably for recognition of proximal-to-distal trends within a given ore system.
There is an abundance of published trace element data for sphalerite, galena and chalcopyrite in natural systems, yet for a co-crystallized assemblage comprising these base metal sulphides, there is ...no detailed understanding of the preferred host of many trace elements. Laser-ablation inductively-coupled plasma mass spectrometry trace element maps and spot analyses were generated on 17 assemblages containing co-crystallized sphalerite and/or galena and/or chalcopyrite from 9 different ore deposits. These deposits are representative of different ore types, geologic environments and physiochemical conditions of ore formation, as well as superimposed syn-metamorphic remobilisation and recrystallization. The primary factors that control the preferred base metal sulphide host of Mn, Fe, Co, Cu, Zn, Ga, As, Se, Ag, Cd, In, Sb, Te, Tl and Bi are element oxidation state, ionic radius of the substituting element, element availability and the maximum trace element budget that a given sulphide mineral can accommodate. Temperature, pressure, redox conditions at time of crystallization and metal source, do not generally appear to influence the preferred base metal sulphide host of all the trace elements. Exceptions are Ga, In and Sn recrystallized at high metamorphic grades, when the preferred host of Ga and Sn usually becomes chalcopyrite. In more typical lower temperature ores, the preferred host of Ga is sphalerite. Indium concentrations also increase in chalcopyrite during recrystallization. At lower temperatures the partitioning behaviour of Sn remains poorly constrained and shows little predictable pattern among the data here. The results obtained may be used as a tool to assess co-crystallization. If trace element distributions in a given base metal sulphide assemblage match those reported here, and assuming those distributions have not been significantly altered post (re-) crystallization, then it may be suggestive of a co-crystallized assemblage. Such information provides a foundation for novel attempts to develop trace element-in-sulphide geothermometers.
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•Trace element partitioning between co-crystallized sulphides is predictable.•Partitioning primarily depends on factors intrinsic to the elements and sulphides.•Partitioning depends little on external factors such as temperature and pressure.•Only high metamorphic conditions affect the partitioning of some elements.
Laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) has rapidly established itself as the method of choice for generation of multi-element datasets for specific minerals, with ...broad applications in Earth science. Variation in absolute concentrations of different trace elements within common, widely distributed phases, such as pyrite, iron-oxides (magnetite and hematite), and key accessory minerals, such as apatite and titanite, can be particularly valuable for understanding processes of ore formation, and when trace element distributions vary systematically within a mineral system, for a vector approach in mineral exploration. LA-ICP-MS trace element data can assist in element deportment and geometallurgical studies, providing proof of which minerals host key elements of economic relevance, or elements that are deleterious to various metallurgical processes. This contribution reviews recent advances in LA-ICP-MS methodology, reference standards, the application of the method to new mineral matrices, outstanding analytical uncertainties that impact on the quality and usefulness of trace element data, and future applications of the technique. We illustrate how data interpretation is highly dependent on an adequate understanding of prevailing mineral textures, geological history, and in some cases, crystal structure.
Sphalerite is an important host mineral for a wide range of minor and trace elements. We have used laser-ablation inductively coupled mass spectroscopy (LA-ICPMS) techniques to investigate the ...distribution of Ag, As, Bi, Cd, Co, Cu, Fe, Ga, Ge, In, Mn, Mo, Ni, Pb, Sb, Se, Sn and Tl in samples from 26 ore deposits, including specimens with wt.% levels of Mn, Cd, In, Sn and Hg. This technique provides accurate trace element data, confirming that Cd, Co, Ga, Ge, In, Mn, Sn, As and Tl are present in solid solution. The concentrations of most elements vary over several orders of magnitude between deposits and in some cases between single samples from a given deposit. Sphalerite is characterized by a specific range of Cd (typically 0.2–1.0
wt.%) in each deposit. Higher Cd concentrations are rare; spot analyses on samples from skarn at Baisoara (Romania) show up to 13.2
wt.% (Cd
2+
↔
Zn
2+ substitution). The LA-ICPMS technique also allows for identification of other elements, notably Pb, Sb and Bi, mostly as micro-inclusions of minerals carrying those elements, and not as solid solution. Silver may occur both as solid solution and as micro-inclusions. Sphalerite can also incorporate minor amounts of As and Se, and possibly Au (e.g., Magura epithermal Au, Romania). Manganese enrichment (up to ∼4
wt.%) does not appear to enhance incorporation of other elements. Sphalerite from Toyoha (Japan) features superimposed zoning. Indium-sphalerite (up to 6.7
wt.% In) coexists with Sn-sphalerite (up to 2.3
wt.%). Indium concentration correlates with Cu, corroborating coupled (Cu
+In
3+)
↔
2Zn
2+ substitution. Tin, however, correlates with Ag, suggesting (2Ag
+Sn
4+)
↔
3Zn
2+ coupled substitution. Germanium-bearing sphalerite from Tres Marias (Mexico) contains several hundred ppm Ge, correlating with Fe. We see no evidence of coupled substitution for incorporation of Ge. Accordingly, we postulate that Ge may be present as Ge
2+ rather than Ge
4+. Trace element concentrations in different deposit types vary because fractionation of a given element into sphalerite is influenced by crystallization temperature, metal source and the amount of sphalerite in the ore. Epithermal and some skarn deposits have higher concentrations of most elements in solid solution. The presence of discrete minerals containing In, Ga, Ge, etc. also contribute to the observed variance in measured concentrations within sphalerite.
Laser ablation-inductively coupled plasma-mass spectrometry and electron-probe microanalysis were used to investigate the trace-element contents of sphalerite, chalcopyrite and pyrite from the Plaka ...Pb–Zn–Ag deposit. Using petrographic observations, the analytical results could be linked to the temporal evolution of the Plaka ore-forming system. Sphalerite chemistry reliably records the temperature and
f
S
2
evolution of the system, with estimated formation temperatures reproducing the microthermometric results from previous fluid-inclusion studies. Chalcopyrite chemistry also shows systematic variations over time, particularly for Cd, Co, Ge, In, Sn and Zn concentrations. Measurable pyrite was only found in association with early high-temperature mineralisation, and no clear trends could therefore be identified. We note, however, that As and Se contents in pyrite are consistent with formation temperatures estimated from co-existing sphalerite. Statistical analysis of the sphalerite data allowed us to identify the dominant geological controls on its trace-element content. The three investigated factors temperature,
f
S
2
, and sample location account for > 80% of the observed variance in Mn, Fe, Co, Ga, Ge, In, Sb and Hg concentrations, and > 60% of the observed variance in Cd and Sn concentrations. Only for Cu and Ag concentrations is the explained variance < 50%. A similarly detailed analysis was not possible for chalcopyrite and pyrite. Nevertheless, comparison of the results for all three investigated minerals indicates that there are some systematic variations across the deposit which may be explained by local differences in fluid composition.
The Hillside Cu–(Au) deposit, Yorke Peninsula, South Australia, is a recently-discovered ore system within the 1.6Ga World-class Olympic iron oxide–copper–gold (IOCG) Province. The deposit is ...characterized by a skarn-style alteration zone. Analyses of feldspar, calcite, skarn minerals (garnet, pyroxene, clinozoisite and actinolite) and accessories (titanite, apatite and allanite), and grain-scale element mapping by laser-ablation inductively-coupled plasma mass spectrometry are used to assess the distributions of rare earth element (REE), incompatible and ore-forming elements in host rocks, prograde and retrograde skarn.
Garnet is a major repository of HREE, especially in prograde skarn, whereas LREE-enriched clinozoisite is the principal REE-host in retrograde skarn. REE distribution patterns define a pronounced partitioning of elements among the dominant coexisting minerals. Compositional variation between assemblages, and also within individual grains, defines an evolution from early feldspar–pyroxene skarn through main-stage calcic skarn to the ore-stage. A switch from a prograde, HREE-dominant signature to a LREE-enriched signature is observed in both retrograde and distal skarn. Zr-in-titanite geothermometry supports transition from magmatic to hydrothermal, skarn-forming processes at temperatures of ~660°C; the initiation of ore-stage is about 100°C lower.
Understanding REE distributions in all minerals within a complex, multistage ore system assists the development of vectoring tools that use trace element chemistry in exploration for similar IOCG deposits beneath regolith cover across the Olympic Province. Titanite and apatite show particular promise because of their characteristically distinct REE patterns in magmatic and hydrothermal stages, trace element responses to redox changes, and their widespread abundance throughout different lithologies in the area.
•Trace element signatures are mapped in skarn minerals at the Hillside IOCG deposit.•REY patterns trace the magmatic- to metasomatic evolution of the system.•REY patterns in titanite and apatite show promise as exploration vectors.
The role of polymetallic melts in scavenging ore components has recently been highlighted in the context of fluid-poor metamorphosed ore deposits. In contrast, the role of polymetallic melts in ...systems dominated by hydrothermal fluids remains poorly understood. Using a simple Au–Bi model system, we explored experimentally whether such polymetallic melts can precipitate directly from a hydrothermal fluid, and investigated the ability of these melts to scavenge Au from the solution. The experiments were conducted in custom-built flow-through reactors, designed to reproduce a hydrothermal system where melt components are dissolved at one stage along the flow path (e.g., Bi was dissolved by placing Bi-minerals along the fluid path), whereas melt precipitation was caused further along the flow path by fluid–rock interaction. Bi-rich melts were readily obtained by reaction with pyrrhotite, graphite or amorphous FeS. When Au was added to the system, Bi–Au melts with compositions consistent with the Au–Bi phase diagram were obtained. In the case of fluid reaction with pyrrhotite, epitaxial replacement of pyrrhotite by magnetite was observed, with textures consistent with an interface-coupled dissolution–reprecipitation reaction (ICDRR). In this case, the metallic melt precipitated as blebs that were localized at the replacement front or within the porous magnetite.
Direct fractionation of Bi–Au melts from a hydrothermal fluid, or precipitation of a Bi-melt followed by partitioning of Au from ambient fluid, offer new pathways to the enrichment of minor ore components such as Au, without requiring fluid saturation with respect to a Au mineral. This mechanism can explain the strong geochemical affinity recognized between Au and low-melting point chalcophile elements such as Bi in many gold deposits. Examples of deposits where such a model may be applicable include orogenic gold deposits and gold skarns. Contrary to models involving migration of polymetallic melts to explain element remobilization, only small quantities (ppm) of polymetallic melts are required to affect the Au endowment of a deposit via interaction with a hydrothermal fluid. The experiments also show that micro-environments can play a critical role in controlling melt occurrences. For example, reaction fronts developing via ICDR reactions can promote melt formation as observed during the replacement of pyrrhotite by magnetite. The associated transient porosity creates space for the melt and promotes melt-fluid exchanges whereas the reaction front provides local geochemical conditions favorable to melt precipitation (e.g., reduced, low
aH
2S(aq), and catalytic surface).
Economic interest in indium (In) and other critical metals has accelerated efforts to understand how such elements occur in nature and the controls on their mineralogy. In this contribution, the ...distribution of In and other trace elements in the Dulong Zn–Sn–In deposit, China, is described, using a holistic approach which targets not only sulfides but also the potential for In and Sn within co-existing oxides and skarn silicates. Sphalerite is the most significant In carrier. Four distinct types of sphalerite are identified, which differ with respect to ore texture and the concentration of In (0.74–4572 ppm). Subordinate amounts of In also occur within chalcopyrite and within andradite garnet, an abundant mineral in the skarn at Dulong and possibly accounting for a significant proportion of total In. Tin is not especially concentrated in either sphalerite or chalcopyrite, occurring instead as cassiterite but with measurable concentrations also in magnetite and skarn silicates. The study confirms that the dominant substitution for In in sphalerite is 2Zn
2+
↔ Cu
+
+ In
3+
but that Ag and Sn may also play a subordinate role in some sphalerite sub-types via the substitution: 3Zn
2+
↔ Ag
+
+ Sn
2+
+ In
3+
. The study highlights that concentrations of In in sphalerite are likely to be heterogeneous at scales from single mineral grains to that of the deposit. The observed partitioning of both In and Sn into skarn silicates, and to a lesser extent, oxides, is a critical factor that may significantly compromise estimations of by-product elements that would be economically recoverable during exploitation of sulfide ores.
Pyrite, the most abundant sulfide on Earth and a common component of gold deposits, can be a significant host for refractory gold. This is the first documentation of pore-attached, composite ...Au-telluride nanoparticles in "arsenic-free" pyrite. Trace elements mapping in pyrite from an intrusion-hosted Au deposit with orogenic overprint (Dongping, China) shows trails of tellurides overlapping Co-Ni-zonation. Intragranular microfracturing, anomalous anisotropy, and high porosity are all features consistent with devolatilization attributable to the orogenic event. The pyrite-hosted nanoparticles are likely the "frozen," solid expression of Te-rich, Au-Ag-Pb-bearing vapors discharged at this stage. Nanoparticle formation, as presented here, provides the "smallest-scale" tool to fingerprint Au-trapping during crustal metamorphism
Constraints on accurate quantitative trace element and sulfur (S) isotope analysis of sulfide minerals, especially pyrite, by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) ...remain imperfectly understood at the present time. Mapping of S isotope distributions within a complex sample containing several minerals requires an evaluation of the matrix effects and accuracy. Here, we apply LA-Q(quadrupole)-ICP-MS and LA-MC(multiple collector)-ICP-MS methods to analyze trace elements and S isotopes in sulfides. Spot analysis of S isotopes was conducted to evaluate the influence of matrix effects. The matrix effects from siderite and magnetite are deemed to be negligible in mapping analysis at the precision of this study. Both Fe and S were used as internal standard elements to normalize trace element concentrations in pyrite. Fe proved to be the better choice because the normalized counts per second ratio of trace elements with Fe is much more stable than if using S. A case study of a sulfide sample from the Chengmenshan Cu deposit, Jiangxi Province, South China, demonstrates the potential of combined S isotope and trace element mapping by LA-(MC)-ICP-MS. The results suggest that this deposit underwent multi-stage ore formation. Elements, including Au and Ag, were hosted in early-stage pyrite but were re-concentrated into multi-component sulfide assemblages during a late-stage hydrothermal event, which also led to crosscutting veins containing pyrite largely devoid of trace elements, except Se. Combining in situ S isotope and trace element analysis on the same sample represents a powerful tool for understanding ore-forming processes.
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