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Soal

Dari informasi sayatan penampang dan analisis data bor untuk tambang open pit bijihbesi seperti yang terlihat pada gambar dihalaman sebelah,hitunglah estimasi cadangan

bijihnya dan kadar rata-ratanya. Hitunglah pula volume soil dan batuan (overburden)

serta stripping rationya. Data kedalaman diberikan disebelah kiri dan kadarnya dalam

persen disebelah kanan. Area yang dilingkari diukur dengan planimeter (dalam satuan

inch

2

). Gunakan factor tonase 14,0 feet

3

/long tonne (0,390 m

3

/tonne). Hitunglahkalkulasinya dalam bentuk table dan tunjukkan langkah-langkah kerjanya!

Jawab :

Diketahui : Faktor Tonase = 14,0 feet3/long tonne (0,390 m3/tonne)

Gambar penampang dan sayatanDitanya:

- Hitunglah estimasi cadangan bijihnya dan kadar rata-ratanya

- Hitunglah pula volume soil dan batuan (overburden) serta

stripping rationya

- Hitunglah kalkulasinya dalam bentuk table dan tunjukkan langkah-

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Section 1 + 00

DH 1 Included area

Noselang

kedalaman(D)(feet)kadar(%Fe) D x % Fe

lebar pengaruh (w)(feet) w x %Fe

Kadar rata-ratapembobotan

w x D(feet2) w x D x % Fe

1 5 58 290 40 2320

57

200 11600

2 5 60 300 40 2400 200 12000

3 5 53 265 40 2120 200 10600

jumlah 15 855 120 6840 1200 34200

DH2 Included area

Noselang

kedalaman(D)(feet)kadar(%Fe) D x % Fe

lebar pengaruh (w)(feet) w x %Fe

Kadar rata-ratapembobotan

w x D(feet2) w x D x % Fe

1 5 59 295 90 5310

57.66666667

450 265502 10 61 610 90 5490 900 54900

3 5 58 290 90 5220 450 26100

4 5 53 265 90 4770 450 23850

5 5 54 270 90 4860 450 24300

jumlah 30 1730 450 25650 2700 155700

DH3 Included area

Noselang

kedalaman(D)(feet)kadar(%Fe) D x % Fe

lebar pengaruh (w)(feet) w x %Fe

Kadar rata-ratapembobotan

w x D(feet2) w x D x % Fe

1 5 60 300 50 3000

43.66666667

250 15000

2 7 56 392 50 2800 350 196003 4 55 220 50 2750 200 11000

4 5 53 5 50 2650 250 13250

jumlah 21 917 200 11200 1050 58850

Section 3 + 00

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DH4 Included area

Noselang

kedalaman(D)(feet)kadar(%Fe) D x % Fe

lebar pengaruh (w)(feet) w x %Fe

kadar rata-ratapembobotan

w x D(feet2)

w x D x %Fe

1 5 61 305 50 3050

57.61538462

250 15250

2 5 57 285 50 2850 250 142503 3 53 159 50 2650 150 7950

jumlah 13 749 150 8550 650 37450

DH5 Included area

Noselang

kedalaman(D)(feet)kadar(%Fe) D x % Fe

lebar pengaruh (w)(feet) w x %Fe

kadar rata-ratapembobotan

w x D(feet2)

w x D x %Fe

1 5 60 300 110 6600

55.64864865

550 33000

2 5 56 280 110 6160 550 30800

3 8 57 456 110 6270 880 50160

4 4 52 208 110 5720 440 22880

5 5 58 290 110 6380 550 31900

6 5 53 265 110 5830 550 291507 5 52 260 110 5720 550 28600

jumlah 37 2059 770 42680 4070 226490

DH 6 Included area

Noselang

kedalaman(D)(feet)kadar(%Fe) D x % Fe

lebar pengaruh (w)(feet) w x %Fe

kadar rata-ratapembobotan

w x D(feet2)

w x D x %Fe

1 5 58 290 90 5220

57.6

450 26100

2 5 62 310 90 5580 450 27900

3 5 59 295 90 5310 450 26550

4 5 55 275 90 4950 450 24750

5 5 54 270 90 4860 450 24300

jumlah 25 1440 450 25920 2250 129600

DH 7 Included area

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Noselang

kedalaman(D)(feet)kadar(%Fe) D x % Fe

lebar pengaruh (w)(feet) w x %Fe

kadar rata-ratapembobotan

w x D(feet2)

w x D x %Fe

1 5 59 295 30 1770

56.66666667

150 8850

2 5 56 280 30 1680 150 8400

3 5 55 275 30 1650 150 8250jumlah 15 850 90 5100 25500

Section 6 + 00

DH 8 Included area

Noselang

kedalaman(D)(feet)kadar(%Fe) D x % Fe

lebar pengaruh (w)(feet) w x %Fe

kadar rata-ratapembobotan

w x D(feet2)

w x D x %Fe

1 5 55 275 30 1650

53.76923077

150 8250

2 5 53 265 30 1590 150 7950

3 3 53 159 30 1590 90 4770

jumlah 13 699 90 4830 450 20970

DH 9 Included area

Noselang

kedalaman(D)(feet)kadar(%Fe) D x % Fe

lebar pengaruh (w)(feet) w x %Fe

kadar rata-ratapembobotan

w x D(feet2)

w x D x %Fe

1 5 59 295 80 4720

56

400 23600

2 5 58 290 80 4640 400 23200

3 5 57 285 80 4560 400 22800

4 5 55 275 80 4400 400 22000

5 5 55 275 80 4400 400 22000

6 5 52 260 80 4160 400 20800

jumlah 30 1680 480 26880 390 134400

DH 10 Included area

No selang kadar D x % Fe lebar pengaruh (w) w x %Fe kadar rata-rata w x D w x D x %

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kedalaman(D)(feet) (%Fe) (feet) pembobotan (feet2) Fe

1 5 60 300 100 6000

55.41176471

500 30000

2 5 56 280 100 5600 500 28000

3 5 59 295 100 5900 500 29500

4 3 55 165 100 5500 300 165005 6 54 324 100 5400 600 32400

6 10 52 520 100 5200 1000 52000

jumlah 34 1884 600 33600 2400 188400

DH 11 Included area

Noselang

kedalaman(D)(feet)kadar(%Fe) D x % Fe

lebar pengaruh (w)(feet) w x %Fe

kadar rata-ratapembobotan

w x D(feet2)

w x D x %Fe

1 5 58 290 50 2900

56.25

250 14500

2 5 58 290 50 2900 250 14500

3 5 57 285 50 2850 250 14250

4 5 52 260 50 2600 250 13000

jumlah 20 1125 200 11250 1000 56250

Section 7 + 50

DH 12 Included area

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KADAR RATA-RATA PEMBOBOTAN & KADAR RATA-RATA

Perhitungan Section 1+00DH1

Kadar rata-rata pembobotan =

D

%Fe)x(D =

feet

feet

15

%855 = 57 %

Kadar rata-rata =

w

%Fe)x(w =

120feet

6840feet% = 57%

DH2

Kadar rata-rata pembobotan =

D

%Fe)x(D =

feet

feet

30

%1730 = 57,66667%

Kadar rata-rata =

w

%Fe)x(w =

feet

feet

450

%25650 = 57%

DH3

Kadar rata-rata pembobotan =

D

%Fe)x(D =

feet

feet

21

%917 = 43,6667%

Kadar rata-rata =

w

%Fe)x(w =

feet

feet

200

%11200 = 56 %

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DH6

Kadar rata-rata pembobotan = D

%Fe)x(D =feetfeet

25%1440 = 57,6%

Kadar rata-rata =

w

%Fe)x(w =

feet

feet

450

%25920 = 57,6%

DH7

Kadar rata-rata pembobotan = D

%Fe)x(D =feetfeet

15%850 = 56,6667%

Kadar rata-rata =

w

%Fe)x(w =

feet

feet

90

%5100 = 56,667%

Kadar rata-rata pada section 3 + 00 =

Dxw

%Fe)x(Dxw

=45022504070650

2550012960022649037450

+++

+++=

7420

419040 = 56.47439%

Perhitungan section 6+00

DH8

%F )(D f t%699

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Kadar rata-rata =

w

%Fe)x(w =

feet

feet

200

%11250 = 56,25%

Kadar rata-rata section 6 + 00 =

Dxw

%Fe)x(Dxw

=100034002400390

5625018840013440020970

+++

+++=

7190

400020 = 55.63561%

Perhitungan section 7 + 50

DH 12

Kadar rata-rata pembobotan =

D

%Fe)x(D =

feet

feet

12

%659 = 54,91667%

Kadar rata-rata =

w

%Fe)x(w =

feet

feet

80

%4440 = 55,5%

DH13

Kadar rata-rata pembobotan =

D

%Fe)x(D =

feet

feet

30

%1780 = 59,333%

Kadar rata-rata =

%Fe)x(w =

f t

feet

450

%26680 = 59,228%

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PERHITUNGAN TONASE

inchi feet

koversi inchi ke feet luas (nch2) Lebar (inch) Luas (feet2) Lebar(feet)

2.4 100 24000 20000

3.9 250 39000 50000

3.4 225 34000 45000

2.7 75 27000 15000

catatan 1 inch

200 kaki horizontal

50 vertikal

1 long tonne = 1,016 tonFaktor tonase = 14,0 feet3/long tonne

Tonase section 1+00 = 14,0480000000

= 34285714.29 long tonne =1,016 x 34285714.29 long tonne = 34834285.71 ton

Section Luas Penampang(feet2)Lebar sayatan

(feet)volume(feet3) tonase (long tonne) %Fe kadar Fe rata-rata w x %Fe

1+00 24000 20000 480000000 34285714.29 50.25253

54.9008525

43690

3+00 39000 50000 1950000000 139285714.3 56.47439 82250

6+00 34000 45000 1530000000 109285714.3 55.63561 76560

7+50 27000 15000 405000000 28928571.43 57.24088 42430

jumlah 311785714.3 219.60341 244930

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Tonase section 3+00 = 14,01950000000 = 139285714.3 long tonne =1,016 x 139285714.3 long tonne = 141514285.7 ton

Tonase section 6+00 = 14,01530000000 = 109285714.3 long tonne =1,016 x 109285714.3 long tonne = 111034285.7 ton

Tonase section 7+50 = 14,0405000000 = 28928571.43 long tonne =1,016 x 28928571.43 long tonne = 29391428.57 ton

Jumlah tonase = 311785714.3 long tonne = 316774285.7 ton

PERHITUNGAN OVERBURDEN

Catatan : 1 inch = 200 kaki horizontal

= 50 kaki vertical

Faktor tonase = 14,0 feet3/long tonne

1 long tonne = 1,016 ton

Volume soil batuan = 2054500000 feet3

Volume batuan = 126000000 feet3

OB (overburden) = 2180500000 feet3 = 14,02180500000 =155750000 long tonne = 1,016 x 155750000 = 158242000 ton

section

Luas (inchi2) luas (feet2)

lebar section (feet)

volume (feet3)

soil batuan soil batuan soil batuan

1+00 13.8 1 13800 1000 20000 276000000 20000000

3+00 17.6 1.1 17600 1100 50000 880000000 55000000

6+00 15.4 1 15400 1000 45000 693000000 45000000

7+50 13.7 0.4 13700 400 15000 205500000 6000000

jumlah 60500 3500 2054500000 126000000

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Stripping Ratio (SR) =TONASE

OB= to n7316774285 .

ton158242000

= 0.4995 0.5

Artinya SR = 1 : 2