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Lainejaur, Malå, Lappland, Sweden

The Lainejaur nickel mine was in operation during 1941-45 and produced about 100000 tons of ore averaging 2.20% Ni, 0.93% Cu and 0.1% Co. The deposit is located in a transition zone between metasediments and metavolcanics as most of the base metal deposits in the Skellefte field. The host rock is a gabbro-norite dike which central part is approximately 50 m thick and overlaid by metasediments. In the central parts the metasediments are almost completely replaced by quartz-diorite and quartz-gabbro without any sharp contact to the gabbro-norite.

Grip (1961) differentiates between three different types of ore at Lainejaur: disseminated ore, massive nickel-pyrrhotite ore and nickel arsenic veins. The disseminated ore consists of pyrrhotite and chalcopyrite in the gabbro-norite. The ore is formed in several different stages and riches in the central parts. The massive ore, which was the most important, consists of almost massive and often coarse grained pyrrhotite containing pentlandite together with chalcopyrite and arsenic nickel minerals. The ore occurs on both sides of the gabbro-norite dike. The nickel-arsenic veins consist of a large number of nickel-, arsenic- and sulfide minerals. The veins often radiates from the massive nickel-pyrrhotite ore in which also occasionally occurs. Note that all of the samples below fall into the disseminated ore category according to E. Grip.

Polished slab of the ore (16 cm wide) with pyrrhotite blebs:

Lainejaur bleb 16.0cm01

Partial scan with higher resolution, the pyrrhotite bleb is surrounded by chalcopyrite.

Lainejaur bleb_d02

The blebs contain textbook like pentlandite flames in the pyrrhotite. Most of the flames are found at grain borders. Nic //, Obj. 20x, air, 100 µm bar:


Some are also inside the grain with no relation to the cracks. Nic //, Obj. 20x, air, 100 µm bar:


A more massive pentlandite vein with flames. Nic //, Obj. 20x, air, 100 µm bar:


The rim of the pyrrhotite is formed partly by chalcopyrite in more complex patterns. The grey mineral is magnetite. Nic //, Obj. 20x, air, 100 µm bar:


Left: pyrrhotite with pentlandite flames, right: chalcopyrite with magnetite (dark grey). Nic //, Obj. 20x, air, 100 µm bar:


Complex structure of magnetite replaced by chalcopyrite. Nic //, Obj. 10x, air, 200 µm bar:


Same with higher magnification. Nic //, Obj. 20x, air, 100 µm bar:


The fibrous parts of the host rock turned out to be clinochlore. The fibre like structure is better visible in some of the foots above, nevertheless here is the spot measured and the corresponding micro raman spectrum (black: this sample, blue: Rruff R061080):

Target.Bildschirmfoto 2013-10-22 um 19.44.34

A similar structure. Here the structure is surrounded by pentlandite and pyrrhotite. Nic //, Obj. 10x, air, 200 µm bar:


I found some time to analyze the black non-opaque minerals filling the gaps between the remaining magnetite. The right spot is quartz, the left spot is calcite (or possibly ankerite).


Polished slab with finely distributed ore minerals. Width: 16.5 cm

Lainejaur diss 16.5cm03

Partial scan with higher resolution

Lainejaur diss_d04

In polished section this type of ore is mainly composed of pyrrhotite and pentlandite, chalcopyrite is present only in traces. Besides the small patches, the minerals occurs in droplets and filings of cracks and spaces between the host rock crystals. Nic //, Obj. 20x, air, 100 µm bar:


Nic //, Obj. 20x, air, 100 µm bar:


Nic //, Obj. 20x, air, 100 µm bar:


Single pyrrhotite droplet with pentlandite exsolution. Nic //, Obj. 50x, air, 50 µm bar:


Vein of pyrrhotite with a core of chalcopyrite. (That’s a nice one, isn’t it?) Width: 14 cm, the vein is 5-8 mm thick.

Lainejaur Vein 14cm05

Partial scan with higher resolution

Lainejaur Vein_d106

Partial scan with higher resolution

Lainejaur Vein_d207

The fotos below are from the region with the chalcopyrite core. This part contains a considerable amount of pentlandite in addition to the two visible sulfides. Nic //, Obj. 10x, air, 150 µm bar:


As above, chalcopyrite, pyrrhotite and pentlandite. Nic //, Obj. 10x, air, 150 µm bar:


The chalcopyrite as well as the pentlandite show internal structures. Here the pentlandite first, with what most likely is a beginning conversion to bravoite. Nic //, Obj. 20x, air, 100 µm bar:



And the chalcopyrite with exsolutions of an undetermined mineral and minor pyrrhotite, Nic //, Obj. 20x, air, 100 µm bar:


The same with Nic +, Obj. 20x, air:


The same with Nic + 2°, Obj. 20x, air, 100 µm bar:


An other part of the samples with chalcopyrite and minor pyrrhotite and pentlandite. Nic //, Obj. 20x, air, 100 µm bar:


The same with Nic +, Obj. 20x, air, 100 µm bar:


For further informations on the region these documents might be interesting:

Grip, E. (1961): Geology of the nickel deposit at Lainijaur in northern Sweden. Sveriges geol. unders., Ser. C No. 577.

Martinsson, E.: Geochemistry and Petrogenesis of the Palaeoproterozoic, nickel-copper bearing Lainijaur intrusion, northern Sweden. GFF.118.(1996).97-109

SGU Prospekteringrapport (1991): Vindelgranseleområdet och Skelleftefältets guldmineraliseringar och malmer. PRAP 91057