Geology of the polymetallic volcanogenic Buttle Lake Camp, with emphasis on the Price Hillside, central Vancouver Island, British Columbia, Canada
Creators: name: Juras, Stephen Joseph
Publisher: name: University of British Columbia
Year: 2010

description: The Buttle Lake Camp is a major Paleozoic volcanogenic massive sulphide district in which the relationships between massive sulphide mineralization and associated volcanism are best explained if the ore deposits and associated lithologic units formed in a rift basin generated by rifting in an island arc system. This setting accounts for the marked linear distribution of the massive sulphide bodies, and the presence and distribution of volcanic products from four distinct source areas: a volcanic arc region, a back-arc (or intra-arc) rifting region, and two seamount areas. These interpretations were achieved largely through detailed mapping (1: 2400) of the Price Hillside and the relogging of pertinent drill core. Geology of the Buttle Lake Camp consists of newly proposed, four lowermost formations of the Paleozoic Sicker Group in the Buttle Lake uplift (in order of decreasing age): (1) the Price Formation, a thick sequence of basaltic andesite flows and related breccias; (2) the massive sulphide-bearing Myra Formation, consisting of mainly volcanic and volcaniclastic units; (3) the Thelwood Formations bedded sequence of siliceous tuffaceous sediments, subaqueous pyroclastic deposits and mafic sills; and (4) the Flower Ridge Formation, largely comprising coarse mafic pyroclastic deposits. Significant units within the Myra Formation are the lowermost, largely felsic H-W Horizon which hosts the large H-W deposit; the Lynx-Myra-Price Horizon, which contains two massive sulphide mineralized felsic volcanic units; the ultramafic G-Flow unit; and the uppermost, basaltic Upper Mafic unit. Zircon U-Pb dating yielded a Late Devonian age of 370 Ma for the Myra Formation. Volcanic units in the Price and Myra Formations are grouped into five volcanic series: two mafic to intermediate volcanic series, two felsic volcanic series, and an ultramafic to mafic volcanic series. These volcanic series are the result of at least three distinct and partly contemporaneous magmatic lineages. Source region for the ultramafic to intermediate parental magmas was an upper mantle peridotite variably enriched in large ion lithophile elements but depleted in high field strength elements (relative to N-type MORB). The felsic volcanic series were generated from two distinct sources. One series is from evolved andesitic magma whereas the other is from magma formed by partial melting of lower crustal material.' The Price and Myra Formations represent a general sequence of repeated events comprising: mafic to intermediate arc volcanism; rifting and sulphide mineralization; felsic arc.volcanism; ultramafic to mafic rift volcanism; and volcanogenic sedimentation. The sequence was repeated twice and formed two mineralized horizons (H-W and Lynx-Myra-Price). The Thelwood and Flower Ridge Formations indicate a major change in depositional style and environment from the two underlying units. The Thelwood Formation is a sediment-sill complex underlying mafic volcanic rocks of the Flower Ridge Formation.