Results of LA-ICP-MS sulfide mapping from Algoma-type BIF gold systems with implications for the nature of mineralizing fluids, metal sources, and deposit models

Abstract

Quantitative laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) element distribution maps combined with traverse mode analyses have been acquired on various sulfides (pyrite, pyrrhotite, arsenopyrite) from three Canadian Algoma-type BIF-hosted gold deposits (~4 Moz Au Meadowbank, ≥ 2.8 Moz Au Meliadine district,~6 Moz Au Musselwhite). These data, in conjunction with detailed petrographic and SEM-EDS observations, provide insight into the nature and relative timing of gold events, the presence and implication of trace element zoning regarding crystallization processes, and elemental associations that fingerprint gold events. Furthermore, the use of an innovative method of processing the LA-ICP-MS data in map and traverse modes, whereby the results are fragmented into time-slice data, to generate various binary plots (Ag versus Ni) provides a means to identify elemental associations (Te, Bi) not otherwise apparent. This integrated means of treating geochemical data, along with petrography, allows multiple gold events and remobilization processes to be recognized and their elemental associations determined. The main gold event in each of these deposits is characterized by the coupling of an As-Se-Te-Ag element association coincident with intense stratabound sulfide-replacement of the Fe-rich host rock. Additionally, the data reveal the presence of a later remobilization event, which upgraded the Au tenor, as either non-refractory or refractory type, along fracture networks due to the ingress of subsequent base metal-bearing metamorphic fluids (mainly a Pb-Bi association). Furthermore, the data reveal a stratigraphic influence, as reflected in the elemental associations and the elemental enrichments observed and the nature of the sulfide phase hosting the gold mineralization (arsenopyrite versus pyrite).

Application of La-Icp-Ms Sulfide Analysis and Methodology For Deciphering Elemental Paragenesis and Associations In Addition To Multi-Stage Processes In Metamorphic Gold Settings

“…Based on these observations, two element associations are noted: 1) Bi-Pb-Co; and 2) Sb-Mo. The latter indicates therefore that, with careful observation, LA ICP-MS traverse data can provide information equivalent to element distribution maps but with a much shorter acquisition timeframe (e.g., Morey et al, 2008;Gourcerol et al 2016a). Importantly, we also note that spot analyses cannot provide such meaningful and detailed information and may in fact average out some or all of the details noted here.…”

“…caption to The application and use of the Co and Ni data is illustrated in Fig. 7 using data from several pyrrhotite (n = 10) and arsenopyrite (n = 3) samples from, respectively, the Musselwhite deposit and the Meliadine gold district (Gourcerol et al, 2016a), as well as arsenopyrite from the Beaver Dam deposit (Fig. 3).…”

“…The strenghs of this latter approach are rarely exploited, but a few recent examples of this type of data processing generated at our institution have been presented (e.g., Dostal et al, 2015;Genna and Gaboury, 2015;McDivitt, 2016;Neyedley et al, 2016;Gourcerol et al, 2016a). The advantage of this approach is that it provides a means to identify elemental correlations not readily observed from element distribution mapping, as is illustrated below, and thus enables one to establish an elemental paragenesis for the phase analyzed and thereby the mineralized system.…”

“…In order to demonstrate the effectiveness of the TSD method, we use sulphide datasets gathered from several Canadian orogenic gold deposits with which we are familiar based on our previous field and petrological studies. These include the Archean banded iron formation (BIF) -hosted Meliadine (Nunavut; e.g., Lawley et al, 2015;Gourcerol et al, 2016a, b), Meadowbank (Nunavut; e.g., Janvier et al, 2015;Gourcerol et al, 2016a, b) and Musselwhite (Ontario; e.g., Oswald et al, 2015;Gao et al, 2015;Gourcerol et al, 2016a, b) deposits consisting of sulphide (i.e., arsenopyrite, pyrite and pyrrhotite, respectively) replacement of Fe-rich material (e.g., magnetite), as well as the Phanerozoic metaturbidite-hosted Beaver Dam deposit (Nova Scotia) in which sulphides such as arsenopyrite occur mainly as quartz vein filling (e.g., Kontak et al, 1993;Sangster and Smith, 2007;Kontak et al, 2013).…”

Genesis of Pyrite Concretions: Constraints from Mineral and Geochemical Features of Longtan Formation in Anhui Province, Eastern China

“…In this paper, we tackle this issue from a mineralogical and geochemical perspective of pyrite concretions. Using scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) microscopy-energy dispersive spectrometer (SEM-EDS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses [16][17][18], we identified the composition of nucleus and rims of pyrite concretions and proposed that pyrite concretions were formed in multiple stages of diagenesis and metasomatism. This paper offers new insight into the sedimentary conditions of the Longtan Formation.…”