Abstract Outcrops in and near the settlements of Cache Creek and Ashcroft, southern British Columbia (Fig. 1), provide an opportunity to view some of the structures and rocks that help to explain the evolution and amalgamation of the allochthonous terranes of the southern Canadian Cordillera. Sediments and igneous rocks ofthe Cache Creek and Nicola Groups formed in late Paleozoic to late Triassic times in oceanic and island arc settings. The sediments of the Ashcroft Formation were deposited from Early through Middle Jurassic time in an arc-related basin. In Late Jurassic or possibly earliest Cretaceus time, thrust faulting juxtapose Cache Creek-Nicola rocks over Ashcroft strata. This event is thought to have sutured these terranes to Quesnellia of which the Ashcroft Formation is generally considered to be a part. This faulting may havebeen related to the early (Late Jurassic) deformationin the Omineca Crystalline Belt when east-directed thrust faults joined Quesnellia to that crystalline terrane.

Abstract Outcrops in and near the settlements of Cache Creek and Ashcroft, southern British Columbia (Fig. 1), provide an opportunity to view some of the structures and rocks that help to explain the evolution and amalgamation of the allochthonous terranes of the southern Canadian Cordillera. Sediments and igneous rocks ofthe Cache Creek and Nicola Groups formed in late Paleozoic to late Triassic times in oceanic and island arc settings. The sediments of the Ashcroft Formation were deposited from Early through Middle Jurassic time in an arc-related basin. In Late Jurassic or possibly earliest Cretaceus time, thrust faulting juxtapose Cache Creek-Nicola rocks over Ashcroft strata. This event is thought to have sutured these terranes to Quesnellia of which the Ashcroft Formation is generally considered to be a part. This faulting may havebeen related to the early (Late Jurassic) deformationin the Omineca Crystalline Belt when east-directed thrust faults joined Quesnellia to that crystalline terrane.

Abstract A consortium containing halophilic, dissimilatory sulphate-reducing bacteria was enriched from Basque Lake #1, located near Ashcroft, British Columbia, Canada to evaluate the role these bacteria have on the immobilization of soluble gold. The consortium immobilized increasing amounts of gold from gold (III) chloride solutions, under saline to hypersaline conditions, over time. Gold (III) chloride was reduced to elemental gold in all experimental systems. Salinity did not affect gold immobilization. Scanning electron microscopy and transmission electron microscopy demonstrated that reduced gold (III) chloride was immobilized as c. 3–10 nm gold colloids and c. 100 nm colloidal aggregates at the fluid–biofilm interface. The precipitation of gold at this organic interface protected cells within the biofilm from the ‘toxic effect’ of ionic gold. Analysis of these experimental systems using X-ray absorption near-edge spectroscopy confirmed that elemental gold with varying colloidal sizes formed within minutes. The immobilization of gold by halophilic sulphate-reducing bacteria highlights a possible role for the biosphere in ‘intercepting’ mobile gold complexes within natural, hydraulic flow paths. Based on the limited toxicity demonstrated in this experimental model, significant concentrations of elemental gold could accumulate over geological time in natural systems where soluble gold concentrations are more dilute and presumably ‘non-toxic’ to the biosphere.