Paleoredox conditions, hydrothermal history, and target vectoring in the MacMillan Pass base-metal district, Yukon, Canada: 1 – Lithogeochemistry of proximal and distal shales

2021 ◽  
Vol 59 (5) ◽  
pp. 1207-1232
Author(s):  
Claire Leighton ◽  
Matthew I. Leybourne ◽  
Daniel Layton-Matthews ◽  
Jan M. Peter ◽  
Michael G. Gadd ◽  
...  
Keyword(s):  
Base Metal ◽  
Enrichment Factors ◽  
Unconsolidated Sediments ◽  
The Black Sea ◽  
Chemical Compositions ◽  
Organic C ◽  
Bulk Chemical ◽  
Isotope Studies ◽  
Host Rocks ◽  
Base Metal Mineralization

ABSTRACT The MacMillan Pass District in Yukon, Canada, hosts the Tom and Jason clastic sediment-hosted Zn-Pb-Ag-(Ba) deposits. Bulk geochemical paleoredox proxies (Eu/Eu*, Ce/Ce*, Mo, Re/Mo, and Ni/Co) indicate anoxic–dysoxic water column and sulfidic porewater conditions persisted during the Late Devonian deposition of the Lower Earn Group host rocks. Positive Eu/Eu* anomalies (up to 3.31) in sulfide mineralization at the Tom deposit are consistent with relatively high temperature (probably >250 °C), reducing, acidic hydrothermal fluids that infiltrated laterally through unconsolidated sediments proximal to the hydrothermal upflow zone and/or exhaled at the seafloor as moderate- to high-density brines. Molybdenum and U enrichment factors (relative to upper continental crust) and Mo/organic C values are consistent with a moderately restricted basin; Mo/C values fall between those of the Black Sea (highly restricted) and the Framvaren Inlet (moderately restricted). A Ba-rich shale was identified in rocks that are distal and time-equivalent units to the Pb-Zn mineralization; based on the bulk chemical compositions and on previous S and Sr isotope studies, we interpret the baryte in this unit to be largely hydrothermal in origin and perhaps remobilized and reprecipitated during hydrothermal base-metal mineralization.

scholarly journals Geochemical signatures of mineralizing events in the Juomasuo Au–Co deposit, Kuusamo belt, northeastern Finland

2021 ◽  
Author(s):  
Mikael Vasilopoulos ◽  
Ferenc Molnár ◽  
Hugh O’Brien ◽  
Yann Lahaye ◽  
Marie Lefèbvre ◽  
...  
Keyword(s):  
Trace Element ◽  
Sulfur Isotope ◽  
Mineral Chemistry ◽  
Chemical Compositions ◽  
Metasedimentary Rocks ◽  
Metavolcanic Rocks ◽  
Icp Ms ◽  
Stage 1 ◽  
Host Rocks ◽  
Relationship Of

AbstractThe Juomasuo Au–Co deposit, currently classified as an orogenic gold deposit with atypical metal association, is located in the Paleoproterozoic Kuusamo belt in northeastern Finland. The volcano-sedimentary sequence that hosts the deposit was intensely altered, deformed, and metamorphosed to greenschist facies during the 1.93–1.76 Ga Svecofennian orogeny. In this study, we investigate the temporal relationship between Co and Au deposition and the relationship of metal enrichment with protolith composition and alteration mineralogy by utilizing lithogeochemical data and petrographic observations. We also investigate the nature of fluids involved in deposit formation based on sulfide trace element and sulfur isotope LA-ICP-MS data together with tourmaline mineral chemistry and boron isotopes. Classification of original protoliths was made on the basis of geochemically immobile elements; recognized lithologies are metasedimentary rocks, mafic, intermediate-composition, and felsic metavolcanic rocks, and an ultramafic sill. The composition of the host rocks does not control the type or intensity of mineralization. Sulfur isotope values (δ34S − 2.6 to + 7.1‰) and trace element data obtained for pyrite, chalcopyrite, and pyrrhotite indicate that the two geochemically distinct Au–Co and Co ore types formed from fluids of different compositions and origins. A reduced, metamorphic fluid was responsible for deposition of the pyrrhotite-dominant, Co-rich ore, whereas a relatively oxidized fluid deposited the pyrite-dominant Au–Co ore. The main alteration and mineralization stages at Juomasuo are as follows: (1) widespread albitization that predates both types of mineralization; (2) stage 1, Co-rich mineralization associated with chlorite (± biotite ± amphibole) alteration; (3) stage 2, Au–Co mineralization related to sericitization. Crystal-chemical compositions for tourmaline suggest the involvement of evaporite-related fluids in formation of the deposit; boron isotope data also allow for this conclusion. Results of our research indicate that the metal association in the Juomasuo Au–Co deposit was formed by spatially coincident and multiple hydrothermal processes.

Competence and lithostratigraphy of host rocks govern kimberlite pipe morphology

2018 ◽  
Vol 55 (2) ◽  
pp. 130-137
Author(s):  
David E. Newton ◽  
Amy G. Ryan ◽  
Luke J. Hilchie
Keyword(s):  
Host Rock ◽  
Sedimentary Rock ◽  
Kimberlite Pipe ◽  
Crystalline Rock ◽  
Experimental Results ◽  
Compressed Air ◽  
Unconsolidated Sediments ◽  
Final Shape ◽  
Class 1 ◽  
Host Rocks

We use analogue experimentation to test the hypothesis that host rock competence primarily determines the morphology of kimberlite pipes. Natural occurrences of kimberlite pipes are subdivided into three classes: class 1 pipes are steep-sided diatremes emplaced into crystalline rock; class 2 pipes have a wide, shallow crater emplaced into sedimentary rock overlain by unconsolidated sediments; class 3 pipes comprise a steep-sided diatreme with a shallow-angled crater emplaced into competent crystalline rock overlain by unconsolidated sediments. We use different configurations of three analogue materials with varying cohesions to model the contrasting geological settings observed in nature. Pulses of compressed air, representing the energy of the gas-rich head of a kimberlitic magma, are used to disrupt the experimental substrate. In our experiments, the competence and configuration of the analogue materials control the excavation processes as well as the final shape of the analogue pipes: eruption through competent analogue strata results in steep-sided analogue pipes; eruption through weak analogue strata results in wide, shallow analogue pipes; eruption through intermediate strength analogue strata results in analogue pipes with a shallow crater and a steep-sided diatreme. These experimental results correspond with the shapes of natural kimberlite pipes, and demonstrate that variations in the lithology of the host rock are sufficient to generate classic kimberlite pipe shapes. These findings are consistent with models that ascribe the pipe morphologies of natural kimberlites to the competence of the host rocks in which they are emplaced.

Detachment faulting and late Paleozoic epithermal Ag-base-metal mineralization in the Spanish central system

Geology ◽  
1988 ◽  
Vol 16 (9) ◽  
pp. 800 ◽  
Author(s):  
Miguel Doblas ◽  
Roberto Oyarzun ◽  
Rosario Lunar ◽  
Nicolas Mayor ◽  
Jesus Martinez
Keyword(s):  
Base Metal ◽  
Late Paleozoic ◽  
Central System ◽  
Spanish Central System ◽  
Detachment Faulting ◽  
Base Metal Mineralization
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