GEOCHEMISTRY OF SMS AS THE ASSESSED CRITERION FOR THEIR MINERAL RESOURCES POTENTIAL

Seafloor massive sulfides (SMS) of the Mid-Atlantic Ridge (MAR) are represented as a real potential reserve of copper to 2040. The most prospective ore fields are located in the North Atlantic active zone of the MAR. In 2012 Russia signed the fifteen-year Contract for exploration of SMS in the Russian Exploration Area (REA). The stated exploration area amounts to 100 units (10 x 10 km each) with the total area of 10,000 km² in the interval 12^о48’ – 20^o54’ N. The culling of 25 promising blocks will be carried during this period. Geochemical specialization of massive sulfide ores depends on content and ratio of Cu, Zn and Fe. The studied fields are identical and characterized by the following geochemical types: Cu-Fe (41%) Fe-S (39%), Cu-Zn (12%), Zn-Cu (5%), Zn-Fe (3%). The inferred resources (IR) of the different geochemical types were calculated for the main economical metals (see table).

Geochemical type of SMS	Average	content	of	metals		Inferred	resources
	Cu,%	Zn,%	Fe,%	Au,ppm	Cu,kt	Zn,kt	Fe,kt	Au,t
Cu-Fe	16.7	0.4	29.6	4.1	3979	105	12173	77
Cu-Zn	16.2	8.5	22.9	20.0	677	314	1377	54
Zn-Cu	2.2	29.3	12.8	1.2	2	30	12	0.1
Zn-Fe	0.5	15.0	23.2	0.6	11	327	549	1.3
Fe-S	0.3	0.9	38.1	0.7	130	143	19223	31
Total inferred resources of dry ore mass	(TIR)					92 Mt

The analysis has demonstrated that copper content is the main factor in the ore quality. According to predominant geochemical type and content of Cu and Au, all SMS sites may be attributed to the four groups (see table).

Group	Predominant type	Cu,%	Au,ppm	Cu-IR,kt	TIR,Mt
I	Cu-Fe(copper-rich)	28.9	4.4	1493	12
II	Cu-Zn	22.6	19.1	1773	8
III	Cu-Fe	6.1	1.3	909	22
IV	Fe-S	0.9	1.1	625	49

The first two groups of SMS are may be regarded as the 1-st turn perspective objects due to its maximum content and resources of copper (see table). Group I consists Ashadze-1, Pui de Folles. Ashadze-2, Semenov-2, Logatchev-1, Logatchev-2 were combined into group II. Similar to the sulfide deposits on the land by the scale of their gold resources may be compared to average and small deposits (in tons): Ashadze-2 (27.5), Logatchev-1 (22.2), Logatchev-2 (10.8), Semenov-2 (7.1). Formally, group III could be regarded as unique (TIR > 22 Mt). SMS sites of group III have, though, low copper mineral potential and their other parameters need additional studying. As for the main metals, group IV is not of much practical interest at the moment.