Rhodonite showings at Arthur Point were found in the 1960s. The Sea Rose claims were staked in 1982 by A.G. Karup of Bella Coola. A few tonnes of rhodonite were extracted at that time. In 1985, 1989 and 1990 the property was owned by Rhode West Resources, and about 2000 tonnes were removed for jewelry, carving, and tile-grade rhodonite. The property was examined by K.D. Hancock of the B.C. Geological Survey in 1991. Much of the following is taken from his report in Exploration in BC 1991.
The rhodonite quarry exposes a zone 1 to 3 metres wide and about 30 metres long; the bed strikes 130 to 150 degrees. The quality of rhodonite is considered high as it has a bright pink colour and attractive, black manganese-coated fractures. The material has been sold to carvers in the Lower Mainland and Vancouver Island as well as overseas to Asian brokers.
Rhodonite occurs as stratabound zones within black cherts and argillaceous cherts. The mineralized zones have a distinctive, yellow, pockmarked weathering surface. There are five distinct rhodonite layers in the northern bay, including the ore zone, and six layers in the southern bay. The mineralized layers exhibit a distinct symmetrical zoning which is repeated around each layer. These zones consist of an outermost jasperoid chert, and intermediate pistachio-green zone, and a core of rhodonite. Associated minerals include layers of iron and manganese oxides. Hostrocks are black and grey chert.
The outer jasperoid zone has sharp, bedding-parallel contacts with the chert, and appears in layers 1 to 10 centimetres thick. The intermediate zone of pistachio-coloured rock is again mostly chert but also contains a variety of other minerals. Compositional layering is defined by colour, typically pistachio green and yellow. The green layers may contain one or more of the following minerals: quartz, garnet, tremolite/actinolite, epidote, calcite, barite and rhodonite. Rhodonite, where present, occurs at the centre of the jasper and pistachio zones, forming stratabound layers, lenses and strings of blebs. The boundary between rhodonite is either massive or occurs as layers interbedded with pistachio rock. The massive rhodonite is bright pink to reddish pink on fresh surfaces. The weathered surface is typically a black rind of manganese oxide 1 to 10 millimetres thick. Massive rhodonite varies in width from less than a centimetre to about three metres. Thin rhodonite bands, less than 10 centimetres across, typically pinch out over several metres in outcrop. Rhodonite layers wider than 10 centimetres are continuous for distances in excess of 50 metres. Towards the edges of the massive material, there are layers of black rhodonite, grey silica or yellow garnetite. Transverse fractures, filled by black manganese oxide are common. Fractures filled by quartz, calcite, epidote, garnet, chlorite, zoisite, tremolite/actinolite, white mica, plagioclase, and opaque minerals are also present. Rhodonite interbedded with yellow garnetite or silica occurs at the margins of some of the thicker massive rhodonite zones. The yellow colour greatly diminishes the value of the material. Barite is a minor constituent of the rhodonite ore zone.
Arthur Point is situated at the western margin of the Coast Plutonic Complex, which includes plutonic rocks with pendants of gneiss, amphibolite, and other metasedimentary and metavolcanic rocks. The pendant ages range from Devonian through Cretaceous. Most are metamorphosed to greenschist or amphibolite grade. North of Rivers Inlet and east of Calvert Island is a large basalt and greenstone body which hosts the Arthur Point rhodonite deposit. The greenstone is largely derived from mafic tuffs with some argillite and chert.
The rhodonite is folded with the host cherts. The massive rhodonite has been brittly deformed. The mineralized zone is crosscut by basaltic dikes related to a gabbro intrusion.
The age and affinity of host cherts are uncertain. The greenstones are largely derived from volcanic tuffs and related material that is likely Late Paleozoic or Mesozoic in age. The Upper Devonian McLaughlin Ridge Formation of the Sicker Group hosts other rhodonite occurrences on Vancouver Island, which suggests a correlation with the pendant rocks at Arthur Point.
Metamorphism post-dates mineralization. The mineralization appears to be metasomatic and is restricted to discrete favourable horizons. The oxide layers and the mineralized zones have significantly anomalous quantities of barium, strontium, vanadium and cerium. The anomalous levels suggest the source of the oxide layers was hydrothermal vents or black smokers. This could indicate that the layers were distal to either a volcanogenic massive sulphide or sedex type environment.
