Clearcut Mn occurrence, Mount Rhoderick Dhu, Greenwood Mining Division, British Columbia, Canadai

Regional Level Types
Clearcut Mn occurrence	Occurrence
Mount Rhoderick Dhu	Mountain
Greenwood Mining Division	Division
British Columbia	Province
Canada	Country

The Clearcut Mn occurrence is located near the headwaters of Clement Creek, about 1 kilometre north-west of the summit of Mount Rhoderick Dhu, and 13 kilometres north of the City of Greenwood, in the Greenwood Mining Division.
There is a good description of the prospect on the British Columbia “Minfile” site, current to 2025, quoted below:
“The main exposure is a 10-metre long roadcut that displays pink pyroxmangite and rhodonite coated with black manganese oxide. This rock has a sugary texture and grades into quartz-rich rock containing spessartine garnet and light coloured mica.
The host rocks are part of the Upper Paleozoic Knob Hill Group that outcrops [sic] in a southeast trending belt extending from the lower course of Clement Creek to Jewel Lake and thence to the area northwest of Mount Roderick Dhu. The Knob Hill Group consists of a variety of volcanic and sedimentary rocks converted to amphibolite and quartz-mica schists by regional metamorphism. The rocks are medium to fine-grained, medium to dark coloured. Primary structures, such as bedding, are often confused with foliation and gneissosity. The metasedimentary rocks consist of quartz (15 to 90 per cent), plagioclase, biotite and some garnet and magnetite, and less commonly amphibole, chlorite, muscovite and occasionally andalusite. Because of recrystallization, metaquartzites and metacherts cannot be distinguished. The amphibolites generally occur as massive lenses - possibly derived from basaltic lava flows and pyroclastic rocks. Typically, the amphibolites consist of 40 to 70 per cent green amphibole, and smaller amounts of plagioclase, quartz, magnetite and titanite. Epidote, calcite and quartz are present in abundance associated with small veins and fissures.
The Clearcut pyroxmangite/rhodonite occurrence is a stratabound deposit associated with what appears to be the metamorphic equivalent of volcanic rocks and siliceous and pelitic sediments. The absence of the primary detrital textures within the silica-rich host rocks is consistent with a chemical precipitate protolith, either of sedimentary or hydrothermal origin. Many similar manganese deposits are considered distal equivalents of volcanogenic massive sulphide deposits.”
Giles Peatfield comments:
Note that the minerals listed below are those reported from the manganese occurrence only, not from the regionally distributed rocks.
As can be seen from the detailed descriptions below of the minerals reported from the occurrence, there is some uncertainty as to the precise manganese silicate species present. This might make a nice research project for a mineralogically inclined senior undergraduate student. The occurrence is easy to gain access to, and Linda Caron, who prepared an early description of the property, lives nearby in Grand Forks and might well be prepared to act as a guide.
Comments on the Minerals Reported:
Amphibole group: Leitch (1995) wrote that “There are also minor amounts of a bladed, colourless mineral with oblique extinction angle about 15 degrees, that could be ?tremolite [sic]. The crystals are euhedral and up to 0.25 mm long.” Simandl and Church (1996) simply reported ‘amphibole’.
Chalcopyrite: Leitch (1995) reported minor amounts of chalcopyrite in polished thin sections, as well as microscopic inclusions in sphalerite.
Chlorite group: Simandl and Church (1996) reported ‘chlorite’ as an alteration product of biotite.
Feldspar group: Leitch (1995) reported ‘plagioclase’; Simandl and Church (1996), describing the biotite gneiss in contact with the manganese zone, wrote that “The gneiss is grey on fresh surfaces and weathers brown. It is characterized by quart-feldspar leucosomes, 2 to 5 millimetres thick, that form over 70% of the rock, separated by biotite-rich melanosomes, less than 1 millimetre thick, locally forming flaser textures.” No additional information is available regarding the feldspar(s) present.
Garnet group: Leitch (1995) wrote that “Garnet forms euhedral crystals to 1 mm diameter, aggregating in places to masses 0.5 cm across. The garnet has pale brownish colour; red colour in hand specimen suggests an Fe-rich (almandine) composition, but significant Mn (spessartine component) could also be present. The garnets are fractured and, near the outside weathered surface of the section, are altered along fractures to fine intergranular semi-opaque Mn-oxides.” Simandl and Church (1996) reported spessartite [sic – spessartine] garnets, but gave no analytical data. Perhaps they assumed spessartine based on the manganese association.
Graphite: Simandl and Church (1996) mentioned that “Graphite flakes, 2 millimetres in cross-section, were observed along one black, manganese oxide filled fracture.”
Limonite: Leitch (1995) reported numerous occurrences of limonite, generally as a weathering product of sulfides. Simandl and Church (1996) simply reported ‘iron oxide’.
Mica group: There have been several mica group minerals reported, some tentative. Leitch (1995) reported possible biotite and more likely hydrobiotite, based on microscopic study. Simandl and Church (1996) reported biotite, and in addition described “An amber-coloured micaceous lens, about 15 centimetres thick, [that] is exposed for 50 centimetres near the base of the outcrop. It probably consists of phlogopite or vermiculite with individual flakes measuring up to 5 millimetres in diameter.”
Pyrite: Leitch (1995) reported small amounts pyrite in polished thin sections, in part altered to limonite.
Pyrolusite?: Leitch reported possible pyrolusite as a surface stain; Simandl and Church (1996) simply reported ‘manganese oxides’.
Pyroxmangite?: Leitch (1995) mentioned pyroxmangite as an oxide alteration of rhodonite, but since pyroxmangite is a silicate it may be that he was mistaken. Simandl and Church (1996) described the occurrence as ‘pyroxmangite/rhodonite’ because they believed at the time that both minerals might be present, writing that “Detailed microscopic, microprobe and geochemical studies that are in progress are needed to characterize this manganese-rich rock.” Subsequently, Simandl et al. (2001) wrote that “The Clearcut prospect is known to contain both pyroxmangite and rhodonite.” This leads one to believe that the above-mentioned studies had been completed, but in a recent email to Giles Peatfield (24 January 2025), George Simandl wrote “The studies regarding this deposit by BCGS [British Columbia Geological Survey] were prematurely interrupted due to lack of funds at that time (that was the downsizing era at BCGS).” This leaves us in the position of not really knowing what manganese silicates are present here.
Pyrrhotite: Leitch (1995) described a polished thin section where “Rare fine grains of pyrrhotite, with minor pyrite and chalcopyrite, form subhedral aggregates to 0.75 mm (oxidized to limonite near edges of the sample).”
Quartz: This is a major constituent of the host rocks for the manganese occurrence.
Rhodochrosite?: Leitch, describing a polished thin section, wrote that “In places, they [rhodonite crystals] are intergrown with (?altering to or altering from?) fine carbonate, mainly along cracks, cleavages and grain boundaries of the rhodonite. Since the rock does not react to cold dilute HC1, this carbonate may be rhodochrosite.” Simandl and Church (1996) were not sure, and suspected either ‘Mn calcite?’ or ‘rhodochrosite?’; given Leitch’s (1995) comment, rhodochrosite seems more likely.
Rhodonite?: See note above for pyroxmangite. It seems that all that can be said with certainty is that the Clearcut occurrence has pink manganese silicate mineralization.
Sphalerite: Leitch (1995) reported small amounts of sphalerite in polished thin section, often with microscopic chalcopyrite inclusions – the so-called ‘chalcopyrite disease’.

The rock type names are taken from Simandl and Church (1996), who were uncertain about chert, and also used the term ‘metachert’ and opined that the rock appeared similar to ‘gondite’. Linda Caron (email to Giles Peatfield 23 January 2025) was happy with the name chert.

Giles Peatfield
BASc . (Geological Engineering) University of British Columbia 1966.
PhD Queen's University at Kingston 1978.
Worked for Texas Gulf Sulphur / Texasgulf Inc. / Kidd Creek Mines - 1966 to 1985.
Consultant 1985 to 2016

Other Databases

Link to British Columbia Minfile:	082ESE241

Other Regions, Features and Areas containing this locality

References