Information on the host rocks

 

Petrography
Petrochemistry
Structure
Rock Alteration

Mineral Zoning in the Sulfide Orebody at Askot

For reasons of convenience in the description of variation in mineral content, the orebody, as encountered in the adits, is divided into three zones. The inner zone extending from the center of the orebody to about 5 mts, the intermediate zone from 5 to 12 mts, and an outer zone from 12 to 17 mts.

Table 1 shows the distribution of the important sulfide and gangue minerals in the various zones. The results presented in the table are based on modal analyses of polished thin sections of 40 samples collected from the adits.

Table 1. Distribution of important sulfide and gangue minerals in the massive sulfide zone.

Mineral (Percent)

Inner zone (0-5 m)

Intermediate zone (5-12 m)

Outer zone (12-17 m)

Arsenopyrite

15.5

1.75

0.33

Sphalerite

12.5

18

12.5

Galena

5.25

10.5

15

Chalcopyrite

18.75

10.5

5.5

Cubanite

4.5

1.5

-

Pyrite

0.45

1.85

4.91

Quartz

10.35

20.55

32.27

Actinolite

12.14

10.81

4.58

Phlogopite

2.62

7.43

2.16

Epidote

2.75

5.18

3.16

Tourmaline

1.73

1.77

2.62

Apatite

2.62

4.87

7.33

Fluorite

-

0.93

1.41

Sericite

0.5

0.62

7.73

Calcite

10.12

3.18

-

Arsenopyrite, chalcopyrite, cubanite, actinolite, and calcite, reach their peak development in the inner zone. Together they make up about 60 percent of the minerals in this zone whereas sphalerite, galena, and chalcopyrite make up 64 percent of total sulfides. In the intermediate zone, sphalerite, phlogopite, and epidote reach their peak development. They constitute more than 30 percent of the minerals in this zone. Sphalerite, galena and chalcopyrite make up 88 percent of total sulfides in the intermediate zone. In the outer zone galena, pyrite, quartz, tourmaline, apatite, fluorite, and sericite are found in the greatest abundance. They constitute more than 65 percent of the minerals in this zone: sphalerite, galena, and chalcopyrite forming more than 85 percent of the total sulfides. The percentage distribution of the important sulfide and gangue minerals in the various zones is shown in fig. 1.

Yellow limonitic stains, indicative of a mineralized zone trending NNW-SSE in the granitic gneisses, are traceable over a strike length of 700 m along the Gurji Gad near Askot. (Pant and Farooq, 1984). In places the mineralized zone is exposed on the surface. Preliminary mineralogical and textural studies indicate that the sulfide minerals occur as epigenetic replacements and were emplaced by the agency of hydrothermal fluids. The main sulfide minerals in order of decreasing abundance are galena, chalcopyrite, pyrite, and sphalerite. The mineralizing solutions invaded the country rocks along foliation planes and joints, and replaced the rock minerals along grain boundaries, cleavages and fractures. In most cases replacement is readily identified because much of the original phase still remains in the form of 'islands' in the replacing sulfides. The proximity of the Barigaon orebody, about 500 m up the slope of the Gurji valley, is of significance. Sulfide and gangue mineral assemblages of the Barigaon and Gurji mineralization are essentially identical. The emplacement of both orebodies is along the S1 foliation, and the sulfide zones are elongated in the direction of F3 fold axes, roughly trending NW-SE, suggesting thereby an identical structural control. These similarities may be considered to be indicative of a common parentage. In these circumstances, prospects of finding a large and rich lode beneath the one at Barigaon may be considered.

Notes & Handouts

The Himalayas

Kumaon Himalayas

Askot Basemetals

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