Dunite. Prop­er­ties, dis­tri­b­u­tion, and indus­tri­al sig­nif­i­cance

Dunite is one of the impor­tant ultra­ba­sic rocks, char­ac­ter­ized by a high mag­ne­sium con­tent. Due to its unique prop­er­ties, dunite is wide­ly used in var­i­ous indus­tries, includ­ing met­al­lur­gy, chem­i­cal pro­duc­tion, con­struc­tion, and refrac­to­ry man­u­fac­tur­ing.

Dunite is includ­ed in the list of min­er­als of nation­al impor­tance approved by Res­o­lu­tion of the Cab­i­net of Min­is­ters of Ukraine No. 827 of Decem­ber 12, 1994 as a raw mate­r­i­al for refrac­to­ries.

Properties of dunite

Dunite is a ful­ly crys­talline intru­sive rock rich in mag­ne­sium, com­posed of an asso­ci­a­tion of min­er­als: olivine, chromi­um spinel, diop­side, horn­blende, gar­net, ensta­tite, clinopy­rox­ene, apatite, plat­inum, sul­fides, and zir­con. Its prac­ti­cal val­ue is deter­mined by its min­er­al and chem­i­cal com­po­si­tion, enrich­a­bil­i­ty, col­or, and oth­er prop­er­ties.

Dunite is black, dark green, or light green in col­or. Its aver­age chem­i­cal com­po­si­tion (%) is as fol­lows: SiO₂ – 40.49; TiO₂ – 0.02; Al₂O₃ – 0.86; Fe₂O₃ – 2.84; FeO – 5.54; MnO – 0.16; MgO – 46.32; CaO – 0.70; Na₂O – 0.10; K₂O – 0.04; P₂O₅ – 0.005; H₂O – 2.88. The den­si­ty of dunite is 3.28 g/cm³. The main mechan­i­cal char­ac­ter­is­tics of the rock include Young’s mod­u­lus, which varies between 0.89 and 1.95×10⁵ MPa, shear mod­u­lus – 0.476–0.706×10⁵ MPa, and Pois­son’s ratio, which ranges from 0.16 to 0.40.

Dunites are com­mon in dunite-harzbur­gite and dunite-clinopy­rox­en­ite-gab­bro com­plex­es found in fold­ed regions. In plat­form areas, these rocks occur in lay­ered intru­sions and ring-shaped alka­line-ultra­ba­sic com­plex­es.

Distribution in Ukraine

Ukraine, with its devel­oped met­al­lur­gy indus­try, needs refrac­to­ries made of dunite and forsterite, but its own raw mate­r­i­al base is hard­ly used. Dunites on the Ukrain­ian Shield (US) were first dis­cov­ered by A. Ya. Kanevsky in 1968. Fur­ther research was con­duct­ed only from a geo­log­i­cal, pet­ro­graph­ic, min­er­alog­i­cal, and geo­chem­i­cal point of view.

The fol­low­ing struc­tures are poten­tial­ly promis­ing for the dis­cov­ery of indus­tri­al dunite deposits:

Golo­vanivs­ka struc­ture
The ultra­maf­ic rocks of the hyper­b­a­site for­ma­tion with­in Ukraine include ore occur­rences and deposits of chromite ores, where dunite rocks were assessed as a com­pan­ion min­er­al. The chromite ultra­ba­sic mas­sifs of the Kap­i­tanivskyi ore field are rep­re­sent­ed by steeply dip­ping bod­ies of dyke and pipe-like shape. The mas­sifs have a dif­fer­en­ti­at­ed lay­ered struc­ture and are enriched with sul­fides. The ore-bear­ing for­ma­tion is rep­re­sent­ed by ser­pen­tinized dunites, peri­dotites, harzbur­gites, and lher­zo­lites, as well as vein pyrox­en­ites, hyper­s­then­ites, and bronzites.

Devladi­vs­ka fault zone
This zone extends sub­lat­i­tu­di­nal­ly through the cen­tral part of the Mid­dle Dnieper megablock. With­in its bound­aries, dunites togeth­er with peri­dotites, pyrox­en­ites, gab­bros, and troc­to­lites form the Archean gab­bro-norite-ultra­ba­sic com­plex. Ore bod­ies are small in size and pre­dom­i­nant­ly dyke-like in shape.

Tik­it­s­ka struc­ture
Dunites in this struc­ture are devel­oped among peri­dotites and ser­pen­tinites. The main deposits are locat­ed near the vil­lage of Koro­liv­ka and in the Chep­izhin­sky ultra­ba­sic mas­sif in the Kirovo­grad region.

Mid­dle Dnieper green­stone struc­tures
This group includes mapped deposits such as Barvinkove, Sukho­hutirsk, Alferivsk, Prav­dyn­sk, and oth­ers. These deposits con­sist of ultra­ba­sic intru­sions rep­re­sent­ed by dunites, peri­dotites, and pyrox­en­ites.

Pri­a­zovskyi megablock
In this zone, dunites are spa­tial­ly asso­ci­at­ed with tec­ton­ic faults and large block struc­tures. Meta­mor­phosed ultra­b­a­sites are mapped in the Obitochnaya, Kiltichya, and Ber­da riv­er basins. The main promis­ing areas include Bur­ty­chya, Balk Krym­skaya, Rodi­onovskaya, and Kamyshu­vatskaya.

Key promis­ing areas with­in the Azov megablock:

• The Bur­ty­chchia area is locat­ed 1.5 km east of the vil­lage of Sofi­iv­ka in the Berdian­sk dis­trict of Zapor­izhzhia region (Kiltichia Riv­er basin). Meta­mor­phosed ultra­b­a­sites are local­ized here among gneiss-gran­i­toid com­plex­es of the Archean and Pale­o­pro­tero­zoic. Their indus­tri­al sig­nif­i­cance has not been estab­lished.
• The Bal­ka Krym­s­ka site is locat­ed 25 km north­east of the city of Berdian­sk and 3.5 km west of the vil­lage of Rodi­on­iv­ka. It is asso­ci­at­ed with the Sorokin­sky tec­ton­ic zone. The rocks are rep­re­sent­ed by meta­mor­phosed vol­canogenic-sed­i­men­ta­ry for­ma­tions of the Archean and Pale­o­pro­tero­zoic. The esti­mat­ed resources of metaultra­b­a­sites are esti­mat­ed at 24.4 mil­lion tons.
• The Rodi­on­ivs­ka site is locat­ed near the vil­lage of Rodi­on­iv­ka in the Berdian­sk dis­trict of the Zapor­izhzhia region. The site con­tains high­ly mag­ne­sian metaultra­b­a­sites, which have not yet been stud­ied in detail.
• The Kamyshu­vatskaya deposit is locat­ed 3 km north­east of the vil­lage of Andri­iv­ka and 48 km north of the city of Berdian­sk. It is locat­ed in the north­west­ern part of the Sorokin­sky tec­ton­ic zone. Ultra­ba­sic rocks are rep­re­sent­ed by chlo­rite-acti­no­lite, tremo­lite-acti­no­lite rocks, and pyrox­en­ites. Esti­mat­ed resources are esti­mat­ed at 47.5 mil­lion tons. Tech­no­log­i­cal tests have shown the pos­si­bil­i­ty of using these rocks to pro­duce forsterite refrac­to­ries.

Application of dunite and forsterite

Dunite has a wide range of appli­ca­tions due to its prop­er­ties. Fine­ly ground dunite is used as a fer­til­iz­er for acidic soils. In some coun­tries, dunite is used as ore for the pro­duc­tion of metal­lic mag­ne­sium. If large blocks of the min­er­al are avail­able, it can be sold as build­ing stone.

Dunites con­tain­ing lit­tle sil­i­ca and a lot of mag­ne­sium are used as high-qual­i­ty refrac­to­ries in met­al­lur­gy and the elec­tri­cal engi­neer­ing indus­try. Crushed dunite is a source of forsterite, chrom­spino­lite, ser­pen­tine, zir­con, and oth­er use­ful min­er­als. Dunite has a vari­ety of col­ors: light gray, yel­low-green, green, or almost black, and can be por­phyrit­ic or striped. Some vari­eties are used as dec­o­ra­tive and fac­ing stone.

Dunite rocks con­tain deposits of var­i­ous min­er­als: chrysotile asbestos, mag­ne­site, uvarovite, chryso­prase, as well as for­ma­tions of nick­el and cobalt for­ma­tions in the weath­er­ing crust. How­ev­er, the main indus­tri­al use of dunite is in the pro­duc­tion of mag­ne­sian olivine – forsterite, which is an impor­tant com­po­nent of refrac­to­ries.

Forsterite (Mg₂SiO₄) is present not only in dunites, but also in peri­dotites, pyrox­en­ites, basalts, car­bon­atites, and mag­ne­sian skarns. It is close­ly asso­ci­at­ed with chromite, chrom­spinels, diop­side, phl­o­go­pite, and plat­inum-bear­ing sul­fides.

Forsterite con­cen­trate is used to make molds for cast­ing non-fer­rous met­als (brass, bronze, alu­minum). Molds made with forsterite sand pro­vide a smooth sur­face for cast­ings and can be reused many times. Fine­ly ground forsterite with mag­ne­sium admix­tures is pressed for lin­ing glass-mak­ing and elec­tric heat­ing fur­naces. Forsterite bricks have high heat capac­i­ty, which allows them to be used to cre­ate heat stor­age con­tain­ers. Forsterite com­petes with quartz sand in foundry pro­duc­tion, where it has advan­tages in envi­ron­men­tal safe­ty and effi­cien­cy, as it does not cause sil­i­co­sis.

There­fore, dunite is a strate­gi­cal­ly impor­tant rock for indus­try, enabling the pro­duc­tion of high-qual­i­ty refrac­to­ries, mag­ne­sium com­pounds, and oth­er mate­ri­als. Ukraine has sig­nif­i­cant reserves of dunite, but their devel­op­ment is still insuf­fi­cient. The devel­op­ment of promis­ing areas, such as the Golo­vanivs­ka struc­ture, the Devladi­vs­ka fault zone, and oth­ers, will allow the coun­try to cre­ate its own min­er­al resource base, reduce its depen­dence on imports, and strength­en its eco­nom­ic poten­tial. This opens up oppor­tu­ni­ties for indus­tri­al devel­op­ment and more effi­cient use of nat­ur­al resources.