Accumulations of hydromagnesite are located within topographic lows immediately east of the community of Atlin. In addition to the two main bodies, a number of small, isolated patches of hydromagnesite occur along the lake shore in the vicinity of Atlin.
The largest deposit is about 7.29 hectares with an average depth of 81 centimetres and it has several smaller satellite bodies. It is located northeast of Atlin, north of the airfield road and lies in a slight depression which opens northwest to a swampy area. Bedrock geology comprises eclogite and mantle tectonites of the upper Mississippian to Permian Cache Creek Complex, and basaltic volcanic rocks of the upper Mississippian to Permian Nakina Formation (Cache Creek Complex).
Glaciofluvial materials underlie the deposit and the basal contact with the underlying clay-like soil and grit is sharp with no evidence of gradation. Near the base of the deposit, however, the hydromagnesite may be more porous and is traversed by irregular vein-like films of glassy hydromagnesite. The surface is slightly raised and hummocky and is crosscut by cracks and fractures up to 3 centimetres wide and 1 metre deep. The bodies are relatively barren of vegetation and have slightly irregular but sharply defined boundaries.
The hydromagnesite is white, powdery and remarkably uniform in texture and composition with no evidence of bedding or structure. The white surface colour assumes a yellow tinge after a depth of about 30 centimetres although this colour disappears with exposure to air. The hydromagnesite becomes quite plastic, like clay, when wet.
Two holes drilled in the deposit were sampled and analyzed. Hole No. 1 indicated a hydromagnesite thickness of 66 centimetres and was sampled at depths of 8, 33 and 58 centimetres. Hole No. 2 indicated a thickness of 1.07 metres and was sampled at 10, 42 and 71 centimetres. Results of this sampling are presented as analytical results for samples 1A, 1B, 1C and 2A, 2B, 2C respectively, in the accompanying table.
A second hydromagnesite deposit lies directly east of Atlin and southwest of the main deposit. It consists of three bodies within topographic depressions and associated with larger areas of impure hydromagnesite. The surfaces of all three bodies are irregular and thickness varies from 0.3 to 2.2 metres. The first body is about 1.82 hectares with an average thickness of about 1 metre but which varies from 0.3 to 1.5 metres. Sample No. 3 was collected at a depth of 53 centimetres near the centre of the body. Sample No. 4 was collected at a depth of 41 centimetres, about 30 metres from site three. The second body is northwest of the first. It is about 0.3 hectare with a variable thickness from 1 to 2.14 metres but averages 1.53 metres. Near the northeast corner of this hydromagnesite deposit the thickness is about 1.73 metres and Sample No. 5 was collected from a depth of 46 centimetres. The material is partly granular and somewhat clay-like with walnut sized, or smaller, pieces of hardened hydromagnesite. Sample No. 6 is a surface sample where the thickness of the deposit is greater than 1.8 metres. The third body constituting this deposit is 0.4 hectare with a thickness of 0.3 to 1 metre. Sample No. 7 was collected about 10 centimetres above the base of the deposit at a depth of 51 centimetres. The material sampled is compact and traversed by thin microveinlets of hydrous magnesium carbonate.
In 1940, unclassified reserves were 107,037 tonnes grading 41 per cent hydromagnesite; 83 per cent of the reserves would grade 41 to 42 per cent MgO. Several hundred tonnes were mined and shipped to the USA between 1904 and 1915.
Analysis of hydromagnesite - Atlin Deposits (Minister of Mines Annual Report 1915):
---------------------------------------------------------------------------------------------------------------------------------------------Sample Deposit Sample MgO CaO SiO2 CO2 Al2O3 Fe2O3 FeO H2O No. Thickness Depth (metres) (cm) 1A 0.66 8 41.13 2.04 1.86 35.98 0.67 0.15 0.60 18.02 1B 0.66 33 42.35 0.82 0.90 36.10 0.10 0.09 0.45 18.95 1C 58 42.19 0.68 0.54 36.17 0.17 0.11 0.64 19.05 2A 1.07 10 40.56 1.26 1.22 35.96 0.67 0.18 0.63 19.04 2B 42 41.93 1.50 1.96 36.04 0.14 0.45 0.65 17.66 2C 71 35.23 6.44 9.22 37.70 0.94 0.73 0.78 8.20 3 1.0 53 42.85 0.32 0.74 36.35 0.35 0.15 0.66 19.10 4 1.0 41 38.94 0.42 3.48 34.31 2.85 0.56 0.81 18.10 5 1.73 46 43.04 0.16 0.96 36.21 0.23 0.12 0.53 19.26 6 >1.83 Surface 43.45 0.26 0.62 36.23 0.41 0.09 0.36 18.95 7 0.61 51 42.12 0.48 1.18 35.89 0.33 0.10 0.71 19.42 ---------------------------------------------------------------------------------------------------------------------------------------------- |
