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Step 3: Determine the percentage of silicon. of calcite. The formula is SG deposit = SG galena (%galena) + SG calcite
(28.09 u Si)(4)
__ 100%Si 4 O 11 = 39.0% Si (%calcite).
×

288.09 u Si 4 O 11
Step 1: Percentage of Galena in Deposit
Hornblende has the higher percentage of silicon.
SG deposit = 3.2
17.7. Use the chemical formula to determine the percent SG galena = 7.5
composition as described in example 10.3. SG calcite = 2.7
Step 1: Write the formula for galena: PbS %galena = ?
Step 2: Determine the formula weight of galena. SG deposit = SG galena (%galena) + SG calcite (%calcite)
and: %calcite = 1 − %galena
Atoms Atomic Weight Total
1 of Pb 1 × 207.2 u = 207.2 u ∴ SG deposit = SG galena (%galena) + SG calcite (1 − %galena)
1 of S 1 × 32.07 u = 32.07 u SG deposit = SG galena (%galena) + SG calcite − SG calcite (%galena)
Formula weight = 239.27 u SG deposit − SG calcite = SG galena (%galena) + SG calcite −
SG calcite (%galena) − SG calcite
Step 3: Determine the percentage of lead.
SG deposit − SG calcite = SG galena (%galena) − SG calcite (%galena)
__ 100%PbS = 86.6% Pb
(207.2 u Pb)(1)
×

239.27 u PbS SG deposit − SG calcite = (%galena)(SG galena − SG calcite )
17.8. (SG galena − SG calcite )
__ __
SG deposit − SG calcite

Chalcopyrite = (%galena)

SG galena − SG calcite (SG galena − SG calcite )
Step 1: Write the formula for chalcopyrite: CuFeS 2
SG deposit − SG calcite

Step 2: Determine the formula weight of chalcopyrite. ∴ %galena = __ × 100

SG galena − SG calcite
Atoms Atomic Weight Total _
(3.2 − 2.7)

1 of Cu 1 × 63.55 u = 63.55 u = (7.5 − 2.7) × 100
1 of Fe 1 × 55.85 u = 55.85 u .05 _
2 of S 2 × 32.07 u = 64.14 u = 4.8 × 100
Formula weight = 183.54 u = 10.4%
Step 3: Determine the percentage of copper. The second step is to determine the mass of the deposit. The
(63.55 u Cu)(1)
__ × 100%CuFeS 2 = 34.6% Cu specific gravity is equal to the density of the deposit in either

3
3
183.54 u CuFeS 2 g/cm or tonne/m . Use the density formula and solve for mass
Chalcocite in tonnes.
Step 1: Write the formula for chalcocite: Cu 2 S Step 2: Mass of Deposit
Step 2: Determine the formula weight of chalcocite. L = 500 m m _

ρ = and V = L × W × H

V
Atoms Atomic Weight Total W = 100 m __
m

2 of Cu 2 × 63.55 u = 127.10 u H = 25 m ρ = (L × W × H)
tonne
1 of S 1 × 32.07 u = 32.07 u ρ = 3.2 _ ∴ m = ρ(L × W × H)

tonne
Formula weight = 159.17 u m 3 = 3.2 _ (500 m × 100 m × 25 m)

m = ? m 3
Step 3: Determine the percentage of copper. _ 3
tonne

= 3.2(500 × 100 × 25) (m )

__ 100%Cu 2 S = 79.9% Cu m 3
(63.55 u Cu)(2)
×

6
159.17 u Cu 2 S = 4.0 × 10 tonnes
Chalcocite has the higher percentage of copper. Then solve for the mass of galena based on its percentage.
17.9. Determine the mass of galena in the deposit by multiplying the Step 3: Mass of Galena
6
total mass of the deposit by the ore grade. m ore = 4.0 × 10 tonnes m galena = m ore (oregrade)
6
oregrade = 10.4% galena = 4.0 × 10 tonnes(0.104)
6
m ore = 1.69 × 10 tonnes m galena = m ore (ore grade) m galena = ? 5
6
ore grade = 8% galena = 1.69 × 10 tonnes(0.08) = 4.2 × 10 tonnes
5
m galena = ? = 1.35 × 10 tonnes Determine the mass of lead by multiplying the mass of galena by
the mass percentage of lead in galena (see exercise 17.7).
Determine the mass of lead by multiplying the mass of galena by
the mass percentage of lead in galena (see exercise 17.7). Step 4: Mass of Lead
5
5
m galena = 1.35 × 10 tonnes m Pb = m galena (%Pb galena ) m galena = 4.2 × 10 tonnes m Pb = m galena (%Pb galena )
5
5
% Pb galena = 86.6% = 1.35 × 10 tonnes(0.866) % Pb galena = 86.6% = 4.2 × 10 tonnes(0.866)
m Pb = ? 5
m Pb = ? = 1.17 × 10 tonnes = 3.6 × 10 tonnes
5

17.11. Read the percentage associated with each mineral from
17.10. Th e first step is to determine the percentage of galena in the ore

Figure 17.13, and calculate the difference to determine the
deposit. Since the average specific gravity of the deposit is a

percentage of each mineral.
function of the combined specific gravities of the minerals in the

deposit, the percentage of galena can be determined by a Mixed amphibole-pyroxene: 100%−70% = 30%
weighted sum calculation. In this case, the specific gravity of the Mixed Na-Ca plagioclase: 70%−0% = 70%

deposit equals the specific gravity of galena times the percentage

of galena plus the specific gravity of calcite times the percentage
678 APPENDIX E Solutions for Group A Parallel Exercises E-36