Copper

There are a large number of copper minerals but the important ones are chalcopyrite (CuFeS2) bornite (CuFeS4) Energite (Cu3As5S4) Chalcocite (Cu2S), Covalite (CuS), Cuprite (Cu2O), Malachite (Cu Co Cu (OH) 2), etc.

The copper minerals are first concentrated and then treated in smelters to purpose the metal which then finds a large number of uses mainly in electrical industries, transport equipment, internal combustion engines and pumps, etc.

At present the concentrators in India are designed to treat only sulfide copper ore and as a consequences the smelters are also designed to treat sulfide copper concentrates only.

As mentioned above copper ore is first concentrated and then smelted to produce copper metal. The price of the metal determines the mill-head grade of ore. Considering the overall economics, the average grade of copper ore is considered as 1% Cu. However, according to HCL at the prevalent prices the mill-head grade of ore of around 1.7% Cu (equivalent to more than 2% Cu as in situ ore) is considered desirable. The specification of the concentrates suitable for treatment at the two flash smelters of HCL are given below:

ITEM

ICC

KCC

Cu %  

22 – 25

14 – 18

Fe %   

28 – 32

32 – 40

S%

29 – 34

28 – 32

Sub-total (%)  

More than 80  

More than 80  

Insoluble (%)

Less than 15

Less than 15

Magnetite (%) 

Less than 8

Less than 8

Moisture (%)

Less than 8

Less than 8

Pb %

Less than 0.5

Less than 0.5

Zn %

Less than 0.5

Less than 0.5

Bi %

Less than 0.01

Less than 0.01

As %   

Less than 0.01

Less than 0.01

Se %

Less than 0.01

Less than 0.01

Te %

Less than 0.01

Less than 0.01

Sb %   

Less than 0.01

Less than 0.01

Size      -           200 mesh

50 – 60%        

60 – 70%        

In the case of copper both cut off and average grades are important. Formerly detailed information regarding cut off grade, average grade, mill feed grade, etc. was not available. But now HCL has supplied information about these parameters and as a result it has been possible to break-up the estimated resources into "reserves" and "Conditional" resources taking in to consideration the cut off and the average grades. The minimum cut-off for estimation of reserves has been taken as 0.45% and the average grade 1% Cu. Problems have been faced in dealing with polymetallic deposits where economics is somewhat complex and a realistic classification of such deposits needs consideration.

After considering the present status and the future trends in technology the following classification of reserves and resources may be considered:

(i)         Reserves                                  :           Cu        1% and above (average)                                                                                                                       0.45% out off (min.)

(ii)        Conditional Resources  :          Cu        (-) 1% (average)

(iii)       Associated metals                     :           Specific grade.

Copper Ore Reserves Classification

1.1 The economics of exploration of ore deposits is dependent on techniques adopted for extraction of desired metals elements or minerals. In the case of copper the ores of copper may be classified as sulfide, oxide and native copper. Of these, sulfide copper ore deposits accounts for most of the world output and most of the above ore types required different techniques and processes for extraction. Sulfide ores after mining are primary treated by crushing, grinding and froth floatation to reduce a concentrate of sulfide minerals. The sulfide concentrates are smelted and electro-refined to produce refined copper. In contrast most oxide ores are not amenable to concentration and are leached by acids and / or bacteria to dissolve the copper. Present industry applications are mainly restricted to previously mined out materials of low-grade and, hence, costs of mining, crushing, grinding, etc., are not included in the costs of such leaching operations. The copper in solution is recovered either by cementation or by electro-winning. Cement copper is treated in a smelter. Electro-won copper is sold as cathodes.

1.2 Copper sulfide ores are sometimes associated with sulfide of other metals like lead, zinc and molybdenum. If other sulfides are occurring in sufficient quantities they are recovered through multistage floatation to produce separate concentrate of different metals.

1.3 In situ leaching of copper ores is another process which is likely to gain importance in future for utilizing copper bearing waste- rocks or low-grade copper ore deposits.

End–product recoveries in different operation may vary as follows:

S. No.

Operations

Recovery %

Remarks

1.

Mining underground Surface grade

70 - 80

Mill-head grade likely to be 75-95% of in situ

2.

Beneficiation

80 - 95

--

3.

Smelting & refining

90 - 95

--

4.

Dump/ head leaching

25 - 50

Production cost does not include previous mining & treatment cost.

5.

Agitation / Vat leaching

More than 50

--

6.

In situ leaching

25 - 50

--

1.4 Since the same cut–off grade of ore may result in different average grades of ores in different deposits, data regarding grade – tonnage variation vis-ΰ-vis cut-off grade changes are essential to estimate recoverable quantity of copper during mining and benefaction operations and / or leaching operations.

1.5 In industrially developed countries a new smelting and refining plant having an annual production capacity of less than 1 lakh tonne of refined Cu is not considered economically viable. Therefore, all mine production that cannot sustain such large production volume has to be toll smelted or marketed in the form of concentrate only.

Since the scale of copper and the technology application determine the cost of production, information, regarding the size of prospective minefield, the average dip of ore-body and resources / reserves per meter depth are important.

Definition of copper ore Reserves/ Resources present status:

The copper ores of the working mines that are located in Bihar, Rajasthan and Madhya Pradesh are predominately consisting of chalcopyrite and pyrhhotite or pyrite. Sizeable quantities of oxidized and predominantly oxide ores occur in Malanjkhand Copper Deposits in Madhya Pradesh. In view of the above composition of copper ores, presently entire mine production is recovered in the form of sulfide concentrate which are treated in two flash smelters at Indian Copper Complex and Khetri Copper Complex. The gross average grade of ores mined by Hindustan Copper Ltd. varies between 1.1% to 1.2% copper. Overall mill recovery is around 90%. The Specification at the two flash smelters are given below:

ITEM

ICC

KCC

Cu %  

22 – 25

14 – 18

Fe %   

28 – 32

32 – 40

Sub-total, Cu + Iron + S (%)

More than 80  

More than 80  

Insoluble (%)

Less than 15

Less than 15

Magnetite (%) 

Less than 8

Less than 8

Moisture (%)

Less than 8

Less than 8

Pb %

Less than 0.5

Less than 0.5

Sn %

Less than 0.5

Less than 0.5

Bi %

Less than 0.01

Less than 0.01

As %   

Less than 0.01

Less than 0.01

Se %

Less than 0.01

Less than 0.01

Sb %   

Less than 0.01

Less than 0.01

Size      -           200 mesh

50 – 60%        

60 – 70%        

At prevalent copper prices and cost of production of copper in the country the mill-head grade of ore of around 1.7% Cu (equivalent to more than 2% in In-situ ore) is considered desirable. However, the in situ grade of reserves in working mines is between 0.95% Cu to 1.79% Cu averaging 1.27% copper. Due to the falling grade in depth in some of the deposits the in-situ average grade of working mines go down in future. The mill-head grade from these deposits taken together is likely to range between 1.2% Cu (present operations) to 1.0% Cu (Future operations).

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