POTENTIAL NATURALLY OCCURRING ASBESTOS IN METAVOLCANIC AND SERPENTINIZED ULTRAMAFIC ROCKS AROUND PARADISE, CA

Naturally occurring asbestos (NOA) is a recognized public health hazard due to the carcinogenic effects of asbestiform minerals when inhaled or consumed. The foothills surrounding Chico have underlying rock formations mapped by the California Geological Survey to contain potential sources of NOA. Examination of unpublished maps, hand samples and thin sections show that the serpentinites are interlayered with metamorphosed ultramafic and mafic “metavolcanic”rocks which are not identified as “potential NOA”. The location and distribution of NOA is important from a public health perspective as to maximize efforts to protect the public and workers from the associated health risks. Sixteen samples were collected from sites that, in the field, were identified as serpentinized ultramafic rocks or metamorphosed mafic metavolcanic rocks. Petrography, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis of metavolcanic and serpentinized ultramafic rocks show the occurrence of both asbestiform amphibole minerals and chrysotile veins. Elongated mineral particles with chemical analysis consistent with amphibole have been identified in the metavolcanic unit north of Paradise, not currently classed as a potential source of NOA. Chrysotile (asbestiform serpentine) veins were observed in the serpentinized ultramafic rock unit, classed as potential NOA, confirming that it is asbestos-bearing. The findings of this study may result in local and statewide reclassification of potential NOA sources.