Physicochemical conditions and timing of rodingite formation: evidence from rodingite-hosted fluid inclusions in the JM Asbestos mine, Asbestos, Québec

Our plain-English summary of Physicochemical conditions and timing of rodingite formation: evidence from rodingite-hosted fluid inclusions in the JM Asbestos mine, Asbestos, Québec, by C. Normand, A.E. Williams-Jones (Geochemical Transactions, 2007).

The study

• Authors: C. Normand, A.E. Williams-Jones
• Journal: Geochemical Transactions
• Published: 2007;8:11
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Fluid inclusions and geological relationships indicate that rodingite formation in the Asbestos ophiolite, Québec, occurred in two, or possibly three, separate episodes during thrusting of the ophiolite onto the Laurentian margin, and that it involved three fluids. The first episode of rodingitization, which affected diorite, occurred at temperatures of between 290 and 360 degrees C and pressures of 2.5 to 4.5 kbar, and the second episode, which affected granite and slate, occurred at temperatures of between 325 and 400 degrees C and pressures less than 3 kbar. The fluids responsible for these episodes of alteration were moderately to strongly saline (approximately 1.5 to 6.3 m eq. NaCl), rich in divalent cations and contained appreciable methane. A possible third episode of alteration is suggested by primary fluid inclusions in vesuvianite-rich bodies and secondary inclusions in other types of rodingite, with significantly lower trapping temperatures, salinity and methane content. The association of the aqueous fluids with hydrocarbon-rich fluids containing CH4 and higher order alkanes, but no CO2, suggests strongly that the former originated from the serpentinites. The similarities in the composition of the fluids in all rock types indicate that the ophiolite had already been thrust onto the slates when rodingitization occurred.

In plain English

This was a geology study, not a health study; it did not examine people, asbestos exposure or disease. The authors studied rodingites, calcium-rich rocks formed where serpentinite altered neighbouring rocks, at the JM Asbestos mine in Asbestos, Québec. They measured how tiny pockets of fluid trapped inside minerals froze and melted, in altered diorite, granite and slate and in vesuvianite-rich veins. In the four samples whose gases were analysed, methane was the main gas, with small amounts of other hydrocarbons, and carbon dioxide was not detected. The authors estimated that diorite was altered at 2.5 to 4.5 kilobars and 286 to 360°C, and granite and veins in slate at 0.6 to 3 kilobars, possibly as hot as 410°C. In one vesuvianite sample (Ves-2), primary fluid pockets of the type labelled 2c became a single fluid on heating at a mean of 191°C. The authors concluded there were probably three episodes of alteration. They noted that their salinity method may overestimate salinity and that a precise age could not be given.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Geological field and laboratory study of fluid inclusions in rocks (heating and freezing measurements under the microscope, and gas chromatography); not a human or animal health study
• Who was studied: Rock samples from the JM Asbestos mine, Asbestos, Québec: four samples of rodingitized diorite, five of rodingitized granite, three rodingites that replaced slate, and two vesuvianite-rich vein samples. Twenty-four thin sections from seven of these samples were studied in detail. No collection dates are given.
• Exposure: No human exposure was studied. The subject was the fluids, trapped in rodingite minerals, that altered rocks in contact with serpentinite.
• Main results:
  • Rodingitization of diorite (samples Dior-1 and Dior-2): estimated pressures between 2.5 and 4.5 kbar and temperatures between 286°C and 360°C
  • Veins cutting rodingitized slate (Slate-1a) and rodingitized granite (Gran-1b): pressures interpreted as between 0.6 and 3 kbar, with temperature potentially as high as 410°C
  • Primary type 2c fluid inclusions in vesuvianite (sample Ves-2) homogenized at a mean temperature of 191°C
  • Type 2a fluid inclusions had salinities of 24 to 27 wt. % equivalent NaCl (5.3 to 6.3 m), uncorrected for clathrate
  • Gas chromatography of the four samples Slate-1a, Gran-1b, Dior-2 and Ves-1 found methane plus ethane, propane, n-butane and n-pentane. Carbon dioxide was not detected in any of these samples.
• The authors' conclusion: The authors concluded that there were probably three episodes of rodingitization. They concluded that the rodingites formed during thrusting of the Asbestos ophiolite onto the Laurentian margin, and they ruled out seawater modified by oceanic mafic magmatism as the source of the fluids.
• Limitations the authors state:
  • Using last ice melting temperatures to estimate salinity may overestimate it.
  • The modelling program considers only NaCl, so the calculated homogenization pressures may be slightly overestimated.
  • A minor gas could not be identified, because nitrogen, carbon monoxide, argon and hydrogen could not be told apart by the method used.
  • The authors estimated an error of about plus or minus 100 bar on the position of the isochores.
  • A precise age for the alteration event could not be given.
  • The exact nature of the fluids awaits more detailed analyses of their dissolved salts.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Jeffrey mine, Asbestos, Quebec

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Rodingite, Ophiolite, Cation, Serpentinite.

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