Marls. Char­ac­ter­is­tics. Vari­eties. Dis­tri­b­u­tion.

Marl is a homo­ge­neous, fine-grained rock that is often some­what plas­tic when wet. Marls are most­ly light in colour, but can also be red, brown and pur­ple. Some marls form nat­ur­al rhyth­mic alter­na­tions with thin clay and sand lay­ers (fly­sch deposits).

Marls may con­tain organ­ic residues, quartz and oth­er min­er­als, sul­phates, iron oxides, glau­conite, etc. as impu­ri­ties. The most typ­i­cal struc­tures of marls are aleu­ropeitic and psamopelitic. Marls are formed by the simul­ta­ne­ous depo­si­tion of clay and car­bon­ate mate­r­i­al.

Marls are sed­i­men­ta­ry rocks that are tran­si­tion­al between car­bon­ate and clay rocks, with a clay par­ti­cle con­tent of 20 to 70%. Typ­i­cal marls con­tain no more than 5% dolomite. Marls are includ­ed in the list of min­er­als of nation­al impor­tance approved by the Res­o­lu­tion of the Cab­i­net of Min­is­ters of Ukraine dat­ed Decem­ber 12, 1994, No. 827, as cement raw mate­ri­als and raw mate­ri­als for sawn wall mate­ri­als.

Properties of marls

Marls are divid­ed into two groups based on their min­er­al com­po­si­tion:
1. Marls con­tain­ing 20 to 40% clay com­po­nent;
2. Clayey marls, in which the index increas­es from 40 to 70%.
Nat­ur­al cement marls con­tain 75 to 80% CaCO3 (the rest is small par­ti­cles of sil­i­cate min­er­als) and can be used in the pro­duc­tion of Port­land cement with­out any addi­tives.

Chem­i­cal com­po­si­tion of marls:
1. The SiO₂ con­tent ranges from 7.99 to 23.10%;
2. Al₂O₃ con­tent ranges from 2.45 — 7.95%;
3. The Fe₂O₃ con­tent ranges from 1.30 — 2.80%;
4. The CaO con­tent ranges from 0.78 — 1.50%;
5. SO₃ con­tent ranges from 0.65 — 1.30%.

Areas of use

Marls, as car­bon­ate rocks, are used in var­i­ous indus­tries, in par­tic­u­lar for the man­u­fac­ture of build­ing mate­ri­als. One of the main appli­ca­tions is the pro­duc­tion of cement for con­struc­tion. Bind­ing mate­ri­als, such as cement, are mixed with water in a pow­dered state, become plas­tic, and then hard­en to form a sol­id stone mass. Some of these mate­ri­als hard­en and retain their strength only in air, such as air lime and build­ing gyp­sum, while oth­ers can hard­en under water, such as hydraulic lime and var­i­ous types of cement.

The process of cement pro­duc­tion involves burn­ing a mix­ture of nat­ur­al lime­stone, clay and marl at a tem­per­a­ture of around 1450℃. The mate­r­i­al is then ground to a fine pow­der, which is the main com­po­nent of cement. Dur­ing the fir­ing process, var­i­ous com­pounds are formed.

Port­land cement is the most impor­tant among the bind­ing con­struc­tion mate­ri­als, as it is char­ac­terised by high strength and fast set­ting. It is a fine pow­der con­sist­ing main­ly of cement clink­er (80–90%), and also con­tains 3–6% gyp­sum and up to 15% active min­er­al addi­tives. For the pro­duc­tion of Port­land cement, marl with a high CaCO₃ con­tent can be used.

Addi­tion­al­ly, it is impor­tant to men­tion sawmill marl. This mate­r­i­al is obtained from marls by saw­ing out ready-made blocks or saw­ing blanks. It is used for cladding exter­nal and inter­nal walls, foun­da­tions and oth­er parts of build­ings and struc­tures.

Deposits in Ukraine

Marl deposits in Ukraine are main­ly con­cen­trat­ed in Donet­sk (Amvrosi­ivske and Karpivske), Ivano-Frankivsk regions and Crimea.

Amvrosi­ivske deposit. It is locat­ed near the rail­way sta­tion of the same name in the upper reach­es of the Bilyi Yar gul­ly, 24 km from the exist­ing plant. The field is com­posed of Mid­dle Car­bonif­er­ous and Cre­ta­ceous rocks; marls are part of the Cam­pan­ian deposits. The thick­ness is up to 140 m, and the depth of the reser­voir bed is 20 to 180 m. The marls are grey, dense, mas­sive, grey­ish-white, loose, frac­tured in the weath­er­ing zone (30–40 m). The min­er­al is under­lain by quartz-glau­conite sand­stones or clayey shales of Car­bonif­er­ous age.

Four types of marls are dis­tin­guished by their CaCO₃ con­tent:

• sandy (СаСО₃ — 55–73%);
• ordi­nary (СаСО₃ 76–78%);
• var­ie­gat­ed (СаСО₃ 65–82%);
• сlay marl (СаСО₃ less than 70%).

The bal­ance reserves (A+B+C₁) amount to 647 mil­lion tonnes, with remain­ing reserves of 346.8 mil­lion tonnes as of 01.01.06. The field is devel­oped by Don­ce­ment OJSC.

Karpivske deposit. The deposit con­sists of chalk, which varies in thick­ness from 3.8 to 43.7 metres (with an aver­age thick­ness of 16.1 metres), and cement marl, which varies in thick­ness from 50.6 to 158 metres (with an aver­age thick­ness of 67.4 metres).
Chalk reserves in cat­e­gories A+B+C₁ amount to 25 mil­lion tonnes, and marl (in cat­e­gories B+C₁) to 105 mil­lion tonnes. At the begin­ning of 2006, the remain­ing chalk reserves were 24 mil­lion tonnes and 103 mil­lion tonnes of marl. The deposit is being devel­oped by Don­ce­ment.

The Mezhy­hirsko-Dubovetske deposit is locat­ed near the town of Halych, Ivano-Frankivsk region. The deposit con­sists of marl lay­ers whose thick­ness ranges from 44.5 to 76.3 m (aver­age thick­ness is 56.0 m). These lay­ers are com­posed of light, bluish and dark grey marls with high den­si­ty, frac­tures and indis­tinct lay­er­ing. Nat­ur­al marls (with CaO con­tent of 40–44%) and clayey marls (with CaO con­tent of 15–40%) are dis­tin­guished. Above the marl lay­ers are gyp­sum lay­ers rang­ing in thick­ness from 0.7 to 7.9 m. Marl reserves in cat­e­gories A+B+C₁ amount to 34.8 mil­lion tonnes, and in cat­e­go­ry C₂ — 47.7 mil­lion tonnes; gyp­sum reserves in cat­e­gories A+C₁ — 3.8 mil­lion tonnes. At the begin­ning of 2006, the remain­ing reserves were 24.9 mil­lion tonnes of marl and 3.8 mil­lion tonnes of gyp­sum. This field is devel­oped by Ivano-Frankivsk Cement.

The Bakhchysaray deposit. The marl deposit is locat­ed near Bakhchysaray on the south­east­ern slope of the third ridge of the Crimean Moun­tains and is com­posed of Eocene marls over­lain by Qua­ter­nary loams.

Min­er­al deposits are rep­re­sent­ed by:

• 1) Qua­ter­nary cal­care­ous loams;
• 2) clay marls of the Almin­ian and upper Kachin­sky stages (CaO 19–41%), rang­ing in thick­ness from 1.0–2.0 to 78.6 m (aver­age 26);
• 3) cal­care­ous marls of the Kachyn­s­ka Suite (CaO over 41.6%), 25.5 to 71.7 m thick (aver­age 54.2).

Thus, Ukraine has sig­nif­i­cant reserves of marl, which are used in con­struc­tion and indus­try, in par­tic­u­lar for cement pro­duc­tion. Marl deposits are dis­trib­uted across dif­fer­ent regions of the coun­try and are rep­re­sent­ed by dif­fer­ent types of marl. In addi­tion, the use of sawn marl for con­struc­tion pur­pos­es, such as wall and foun­da­tion cladding, is wide­spread. Marl deposits are being active­ly devel­oped by indus­tri­al enter­pris­es, which con­tributes to the devel­op­ment of the con­struc­tion and cement indus­try in Ukraine.