GRADE AND TONNAGE MODEL OF SIERRAN KUROKO DEPOSITS
By
Donald A. Singer
COMMENTS
This model applies to the descriptive model for kuroko massive sulfide
(No. 28a)by Singer (1986);
however, only kuroko deposits of Triassic or Jurassic age in North America
were used to construct this subset (table 8). Because many of the deposits
lie in the western foothills of the Sierra Nevada in California, the name
Sierran kuroko is given to the group. These deposits are significantly
smaller in tonnage than the worldwide kuroko group. The reason for this
difference is not known. Estimated pre-mining tonnages and grades or total
production from the deposits listed below were used to construct the model.
Where several different estimates were available for a deposit, the estimated
tonnage associated with lowest cutoff grades was used.
The
breaks in slopes of the lead, silver, gold, and zinc plots (figs. 16-19)
may be related to underreporting of production grades caused by early
ore-processing problems. Silver grade is correlated with gold grade (r
= 0.76, n =16). See appendix
B for locality abbreviations. See introduction
for explanation of the grade and tonnage model as shown in figures
14-19.
Table 8. Grades and tonnages of Sierran kuroko
deposits
[Tonnages
in million metric tons; silver (Ag) and gold (Au) grades in grams per
metric ton; other grades in percent. Country and state abbreviations explained
in appendix B]
Deposit Country
Tonnage
Cu
grade Zn
grade Pb
grade Ag
grade Au
grade
Afterthought
USCA
0.151
3.23
16.15
2.17
190
1
Big
Bend USCA
.05
1.14
10.7
.2
41.4
1.54
Blue
Ledge USCA
.18
4.1
2
0
187
4.3
Blue
Moon USCA
.105
.36
12.5
.45
123
2.09
Bully
Hill-Rising Star USCA
.62
3.8
3.1
0
130
1.98
Copper
Crowrt CNBC
.211
.31
4.25
0
25
0
Copper
Hill USCA
.266
.43
0
0
0
0
Cronin
CNBC
.054
8.12
7.11
0
431
34
Double
Ed CNBC
3.63
1
.6
0
0
0
Duthie
CNBC
.118
.4
6.5
2.8
106.5
1.27
George
Copper CNBC
.553
2
0
0
17.2
2.06
Gray
Eagle USCA
1.33
3.8
0
0
17.6
6.17
Greens
Creek USAK
3.629
.5
9
2.5
343
3.4
Keystone-Union
USCA
1.2
2.37
0
0
.75
.01
Marnie
CNBC
.055
.7
7.6
0
0
11
Newton
USCA
.15
3.51
.2
0
13.6
.17
North
Keystone USCA
.205
2.2
0
0
1.3
.02
Penn
USCA
.884
4.24
1.14
.06
75
2.38
Red
Wing CNBC
.181
2
0
0
0
0
Silver
Queen CNBC
.363
.76
6
2.1
275
3.1
Spenceville
USCA
.136
5
0
0
0
0
Sunshine
CNBC
.313
.18
4.8
1.69
12.2
0
Tulsequah
CNBC
1.62
1.27
6.9
1.26
140
4.04
Figure 14. Tonnages for Sierran kuroko
deposits.
Figure 15. Copper grades for Sierran kuroko
deposits.
Figure 16. Zinc grades for Sierran kuroko
deposits.
Figure 17. Lead grades for Sierran kuroko
deposits.
Figure 18. Gold grades for Sierran kuroko
deposits. (Gold grade for Keystone-Union not shown.)
Figure 19. Silver grades for Sierran kuroko
deposits.
