Heritage Stone 8. Formation of Pinolitic Magnesite at Quartz Creek, British Columbia, Canada: Inferences from Preliminary Petrographic, Geochemical and Geochronological Studies

Rocks in the Late Proterozoic Horsethief Creek Group at Quartz Creek in British Columbia display rare ‘pinolitic’ textures resembling those described in some sparry magnesite deposits elsewhere in the world. Elongated white magnesite crystals up to 30 cm long occur in a contrasting, dark, fine-grained matrix of dolomite, chlorite, organic material, clay minerals and pyrite. The rocks are aesthetically appealing for use in sculpture and as dimension stone. The term ‘pinolite’ is derived from the superficial similarities between these unusual textures and pinecones. Petrographic examination indicates that these textures formed when metasomatic fluids replaced primary sedimentary dolomite with magnesite. Fluids moved along fractures and bedding planes with repeated fracturing yielding magnesite crystals oriented in opposite directions on either side of annealed fractures, and broken magnesite crystals adjacent to later fractures. Magnesite contains dolomite microinclusions and has elevated Ca contents that are consistent with its formation by replacement of dolomite. Low concentrations of Cr, Ni, Co, Ti, Sr, and Ba in magnesite also imply formation in a metasomatic rather than a sedimentary environment. The rare earth element (REE) concentrations in the Quartz Creek magnesite are higher than those in most evaporitic magnesite and REE patterns lack the Ce and Eu anomalies that characterize carbonate rocks from sedimentary environments. Enrichment in light REE relative to heavy REE, and the similarities between dolomite, chlorite, and magnesite REE profiles, imply that metasomatic fluids modified the original sedimentary geochemical signature of the dolostones during formation of the pinolite rocks. A Late Ordovician to Early Silurian U–Pb age (433 ± 12 Ma), for titanite in the black matrix surrounding the sparry magnesite is younger than the local host rocks, and also younger than the Mesoproterozoic to Middle Cambrian stratigraphic ages of the host rocks for nearby magnesite deposits. The ca. 433 Ma titanite overlaps the ages for numerous fault-associated diatremes and volcaniclastic deposits in the area. Possibly the igneous activity furnished heat for, and/or was the source for, metasomatic fluids that produced the pinolite deposits.

Characteristics of Waste Generated in Dimension Stone Processing

Natural dimension stone processing generates large volumes of stone waste, which have a significant impact on the environment, as well as on the efficiency and profitability of the stone-processing plant. The article presents the characteristics of waste produced as a result of natural dimension stone processing and the structure of the waste production process. Solid stone scraps and sludge were distinguished. On the basis of the performed analyses, it was shown that stone waste constitutes 10–35% in relation to the quantity of the processed stone material, with the quantity of sludge being even threefold greater than the volume of solid scraps. According to the circular economy principles, the aim should be to reduce the amount of waste generated by reducing primary resources in favour of secondary material. Reducing the volume of stone waste is possible through rational planning of stone production while at the same time maximising the efficiency of stone material usage and introducing the most modern processing machines. This significant volume of stone waste encourages efforts to find solutions for both its management and reduction. This paper reviews the utility potential of stone waste. Sensible use of waste is important to increase the profitability and productivity of processing plants while incentivising environmental protection.