The Sedimentary Phase that Initiated the Concentrating of Gold Ores, Matachewan-Kirkland Lake-Larder Lake Area, Ontario, Canada

Abstract The Matachewan-Kirkland Lake-Larder Lake gold-copper-ironasbestos-barite mining district is situated in Late Archean rocks of the Canadian Precambrian Shield’s Superior Province, -Abitibi sub-province, southwestern part. The structural setting seems to be comparable to Nevada’s Carlin-Battle Mountain “Basin and Range” zone. Prior to modification and in some places up-grading by both tectonically-induced migration and (or) the metasomatic and heatpump effects of later mafic flows and felsic intrusions, a sedimentary phase was essential. Referring to Archean gold deposits in Australia, Tomich (1990) noted that the successful search for new gold ores requires a stratigraphic approach with a structural approach as a secondary adjunct (i.e. the reverse of present practice). A sedimentary phase initiated the accumulation of what has become the Matachewan-Kirkland Lake-Larder Lake and other similar gold ores. The purpose of the following text is to describe this sedimentary protore-generating phase. The total amount of gold produced from the 100 km-long Matachewan-Kirkland Lake-Larder Lake mining district, from approximately the beginning in 1910 until 1990, was more than 37 million Troy ounces. Most production was selectively mined so that the historical average grade (and in some cases the cut-off grade!) is almost 1/3 of a Troy ounce per short ton (about 10 grams per metric tonne). Among large Canadian gold mining districts this grade is exceeded only by the Northwest Territories (predominantly Yellowknife) and Ontario's Red Lake, and this production only by the Porcupine (Timmins).