Prospecting of Silica of Naudanda Quartzite, West Central Nepal

Abstract

As the importance of silica is increasing in digital world and other sector, prospecting of silica is the initial process for silica exploration. For prospecting of silica, the Naudanda Quartzite was studied thoroughly. The potential of silica content in the Naudanda Quartzite is presented in very few reports and literatures. Therefore, the study was carried out along the Siddartha Highway and other local roads around the Bhalu Pahad area. The area comprises of mainly phyllite, metasandstone and medium- to coarse-grained orthoquartzite of the Lesser Himalayan metasedimentary sequence. Here orthoquartzite is targeted for the prospecting of silica as quartzite constitutes more than 90% quartz minerals. The study was carried out to prospect the silica resource and compute the mineral reserve in the area. From the route map prepared at 1:2,000-scale along the Bhalu Pahad-Haripala section and columnar section, it is found that the true thickness of the Naudanda Quartzite is 760 m. A geological map was prepared at 1:25,000 scale, and 15 quartzite samples were taken from suitable locations preventing stratigraphical reoccurrence. Five samples were taken randomly from folded zone. Silica grains were counted on the basis of fleet method after thin section preparation of 15 individual samples. More than 95% silica is present on an average. Again, silica content of 5 samples out of 15 were tested chemically and found more than 95% silica concentration. For reserve calculation, silica grade was taken 95% and the reserve was computed on the basis of three cross-sections. It is found that the total volume tonnage is 2.6 billion ton of silica content, and concluded that the silica present in the rock is economic and minable.

Introduction

The Lesser Himalaya is the major contrast region with different metamorphosed to unmetamorphosed lithology in the Nepal Himalaya. The study area (Fig. 1) lies in the Syangja District around the trijunction of Phedikhola Gaupalika, Aadhikhola Gaupalika and Putalibazar Nagarpalika, and comprises mainly of crenulated phyllite, grey green phyllite, metasandstone, dolomite, and pale white to white orthoquartzite. Occurrence of silica is most permissible in quartzite as quartzites forms from more than 90% quartz minerals (Hirayama et al., 1988).

Fig. 1. Location map of the study area.

The Naudanda Quartzite falls in the Lesser Himalayan zone, Kaligandaki Supergroup as defined by Sakai (1985). The indications of potential occurrence of silica in the Naudanda Quartzite were justified by the Hirayama et al. (1988). White orthoquartzite is the main characteristics of this formation as from the various literatures (Sakai, 1985; Dhital et al., 2002; Sharma et al., 2024). White orthoquartzite was deposited around Late Precambrian age (Sakai, 1985) in wave-dominated delta environment (Paudyal, 2012) so that the clay mineral was washed away and the pure silica was present. The characteristics of the lithology present in the Naudanda Quartzite can be correlated with the Fagfog Quartzite of the Central Nepal Himalaya (Stöcklin and Bhattarai, 1977; Stöcklin, 1980), Ghandrung Quartzite of Western Nepal, Upper Hokse Quartzite of Arun River window (Andrews, 1985) and Kositar Quartzite of Eastern Nepal. The study is primarily focused on the prospecting of silica and potentiality of silica mining in the future. The main objectives of this research are, to analyze the content of silica mineral in quartzites using petrographic method and gravimetric filtration method, and to find the total silica volume in tonnage. In the Jiajuri Quartzite deposit of India, which has gone through detailed exploration for silica and other parts of India, generally the silica content in the rock is found on the basis of gravimetric method given by IS 1917-3 (1992). Therefore, the silica finding from gravimetric method is quite reliable.

Geology of the Study Area

The study area (Fig. 1) belongs to the Kaligandaki Supergroup defined by Sakai (1985). It basically consists of thinly foliated crenulated dark grey to green phyllite, and thickly foliated medium indurated gritty phyllite with occasional occurrence of metasandstone and quartzite of the Kuncha Formation, medium to thick bedded, ripple laminated fleshy white to white quartzites of the Naudanda Quartzite, and thinly foliated green to dark grey phyllitic slate of the Nayagaun Formation. The little part is covered by the Nourpul Formation comprising of pink quartzite and purple phyllite, and carbonate rock of the Dhading Dolomite.

The Naudanda Quartzite is named from the type locality along the Seti Khola about 4 km northwest of Syangja (Hirayama et al., 1988). The formation consists of fine-to coarse-grained, white quartz arenites (orthoquartzite), which are strongly rippled and cross-bedded and having several interbeds of phyllite, conglomerate and metabasite of the Naudanda Quartzite. The ripple marks are commonly of oscillation type, which indicates the deposition was under a shallow marine environment. Hirayama et al. (1988) also investigated the geology of the Naudanda Area. The main lithology found in this formation is largely of orthoquartzite, associated with subordinate intercalation of slaty phyllite. The color of the quartzite is commonly of white and less commonly of green-grey in fresh parts whereas weathered part of the quartzite seems to be pinkish brown. Hirayama et al. (1988) have tested the chemical composition of the white orthoquartzite of the Naudanda Quartzite from different locations: Guni Khola, north of the Bhat Khola and NW of Putalikhet, and reported oxides of three samples as: SiO₂ (91.66%, 97.11%, and 94.22%), Fe₂O₃ (0.64%, 0.91%, and 0.21%), Al₂O₃ (2.20%, 0.91%, and 0.79%), CaO (4.40%, trace and 2.20%), and MgO (1.20%, 2.02%, and 2.00%). Overall, the silica percentage in the orthoquartzite is very high. Dark-grey to green-grey phyllite of few cm to 5 cm or more is occasionally intercalated with orthoquartzite.

Dhital et al. (2002) investigated the stratigraphy and structure between Kusma and Syangja and reported that, the Naudanda Quartzite lies above the Phalebas Thrust in the Lamae Khola, in the Darung Khola, around Khalte and at Dharampani. Dhital et al. (2002) reported medium to very thick bedded (0.5~5 m), massive, pale yellow, light grey, white and light green quartzites alternating with thin banded, blue green to green grey phyllite and thick, coarse-grained, dark green amphibolite. According to them, the thickness of the Naudanda Quartzite is of 800 m at Naudanda. Geological structures like cross-bedding, ripple marks etc. are primary sedimentary structure and mesoscopic folds, faults and thrust are the secondary structure found in the study area. The Phalebas Thrust is the major geological structure in the study area.

Materials and Methods

The detail study of the Naudanda Quartzite was done from the north cliff of Bhalupahad to the Haripala Village toward the Syangja Bazar along the Siddartha Highway. For the detail study, a route map was made in the scale of 1:2,000 and the quartzite samples from the bedrocks were collected from intended location. The exact location was marked by using GPS and topographic map. Geological map and cross section, and generalized columnar section were made to calculate the height, thickness and eventually total silica deposit in the area. Fifteen quartzite samples were collected at the interval of 40~50 m, and 5 samples were taken randomly as they occurred in the stratigraphic repetition region. Detail columnar sections of each sample bed location were prepared. Thin sections of 15 quartzite samples were prepared for petrography. After thin section preparation, individual grain was counted manually after fleet method and the composition as well as silica percentage were calculated. After petrographic study, suitable 5 samples were taken for the chemical analysis.

Results

Lithology of Naudanda Quartzite

The lithology of the Naudanda Quartzite dominantly comprises of medium-grained white to pale white quartzite with both oscillatory and current ripple marks. This formation overlies the relatively older formation consisting of phyllite, gritty phyllite and occasional metasandstone beds of the Kuncha Formation in normal sequence (Fig. 2). In the lower part of the Naudanda Quartzite, thick bedded (1~2.5 m), medium- to coarse-grained quartzite can be found, while in the middle part relatively medium- to thick-bedded (0.3~1 m), fine- to medium-grained, fleshy white to white quartzite can be found. In the upper part, alternating beds of relatively medium bedded, medium-grained quartzite with grey to black phyllite can be observed. At Ekrahe, one of the villages of the study area, about 4 km west from the Naudanda Bazar, a huge outcrop of green amphibolite of about 40 m breadth can be observed and also about 1 km west from the Chhari Khola Gaun same kind of green amphibolite is observed. It indicates that the Naudanda Quartzite also consists of metabasic rock. Above the Naudanda Quartzite, thinly foliated grey, black, greenish grey slaty phyllite with occasionally well indurated, foliated, green phyllite and metasandstone of the Nayagaun Formation are present.

Fig. 2. Generalized lithostratigraphy of the study area.

Field Observation and Hand Sample Study

The hand sample taken from the outcrop was studied thoroughly. It is found that the overall sample is mostly of medium-grained, yellowish white to white. Under hand lens, dominant mineral is quartz grains exhibiting mosaic, granular, polygonal, and granoblastic texture. Very few amount of biotite, muscovite, iron oxide, feldspar and other minerals are present in dispersive manner. The hand samples are of medium specific gravity, well indurated, non-foliated and gritty. Interlocking grains of the quartz are also bounded by siliceous material. The sample break by making sharp edges and giving the vitreous lustre. Quartz veins are present in few amounts. Dominance of quartz mineral indicates the presence of high percentage of silica in the rock sample.

Petrography

To find the overall percentage of the quartz (silica) grains in the thin section (Fig. 3) of the sample, petrography was done. Here, 15 thin sections were examined and counted approximately 300 grains of almost all the quartz grains, and other present grains, which are greater than 30~50 micro meter, by digital pen placing the photomicrograph in the application called ‘Count Things’. From this the percentage of quartz grain was estimated most precisely though it was tedious. This process is continued to all the fields of view of each sample and average quartz (silica) percentage of the sample was determine, and found that almost in all the sample, quartz percentage is above 95% (Table 1). Table 1, gives the results of petrographic analysis where average quartz and other mineral percentage of each sample and large quartz (QL) >220 micrometer and small quartz (QS) < 220 micrometer in remarks are presented.

Fig. 3.(a) Photomicrograph of sample no. BP 07 containing much high amount of ferruginous oxide, (b) Photomicrograph of sample no. 08 comprising dominantly large quartz, (c) Photomicrograph of sample no. BP 11, (d) Photomicrograph of sample no. BP 13 containing high percentage of feldspar.

Table 1. Results of petrographical analysis

From the above detail study of the samples, the average composition obtained is, quartz = 95.86%, sericite, muscovite and biotite = 1.58%, feldspar = 0.75%, ferruginous oxide = 0.87%, hematite, magnetite = 0.20%, and other minerals = 0.92%. The average large quartz (QL) obtained is 58.56% and small quartz (QS) is of 41.44%. During the study not only the composition was studied but also all the individual sample texture and microstructure were studied. The common textures observed were subhedral to euhedral crystal grains, concavo-convex and sutured contacts among grains, etc (Fig. 3). In the case of microstructure, non-foliated, fractured quartz, recrystallization of quartz in the grain boundary and slightly elongated quartz grain can be seen.

Chemical Test

After detail examination from petrography or modal analysis it is found that overall average silica (quartz) percentage of the sample taken from the quartzite is 95.86%. For the sureness of the silica concentration, certain samples were chosen, and silica concentration was found by chemical analysis called silica test by gravimetric filtration method. Sample BP 02, BP 05, BP 08, BP 11 and BP 13 were tested and very good results have been obtained (Table 2).

Table 2. Silica concentration results from chemical test by gravimetry

From chemical analysis the average silica percentage is found to be 95.12%, which is only 0.75% less than the result obtained from the modal analysis. Here, the test results from the modal analysis and from the chemical test are quite similar, for example, the quartz (silica) percentage acquired from modal analysis of BP 02 is 97.7% and from chemical test is 96.53%, in which only 1.17% difference is recorded, reflecting that the quartz (silica) percent determined for all the samples are valid.

Geological Mapping and Resource Estimation

For the reserve calculation geological map and cross-sections (Figs. 4 and 5) in 1: 25,000 scale were made around the study area by physical survey by taking different adequate traverse along different local roads, trail and the khola present, by taking 9 Km × 7 Km area to find the distribution of quartzite. In the survey, short distance traverse about 4~5 Km in a day (8 Am~5 Pm) was made to get detail information of the area and the dip amount and strike were measured and plotted on the topographic map continuously, and noted all the characteristics description of the outcrop in every interval of 200~300 m in field diary and mobile application named ‘SW Map’. While taking traverse, quartzite was very hard to break with hammer and only certain rock chips were extracted after many blows which directly indicated the high presence of silica mineral. Here the area was already mapped by various researchers (Khanal, 2001; Dhital et al., 2002), but for the verification, detail mapping was done. The lithostratigraphic name are given according to Dhital et al. (2002). The Kuncha Formation, Naudanda Quartzite, Nayagaun Formation, Nourpul Formation, Dhading Dolomite and the Benighat Slates are the lithostratigraphic units mapped in the area (Fig. 4). The Phalebas Thrust is the major fault in the study area and various mineralization like quartz crystal, lead, silver, malachite are noticed around this thrust. The geological map was corrected and improved to the previous geological map, as lithological unit in some portion of the previous map was not distinct.

Fig. 4. Geological map of the Lesser Himalaya in Bhalupahad-Syangja area, West Central Nepal.

After the geological mapping, the area and volume were computed from cross-sectional method (Kumar, 1988). For doing it, three cross-sections were made from the suitable three cross-section lines (Fig. 5). In each cross-sections, mining height was considered as above highway elevation. Therefore, the mining heights of the blocks; M, K, H or cross-sections A-C were 900 m, 1,000 m, and 900 m, respectively and marking this elevation in cross-sections the actual minable quartzite was found. The cross-sections were made on graph paper, so the area occupied by the minable quartzite was computed by measuring the polygons present in the graph with precisely and accurately. Here the measured area was not totally quartzite as quartzite was associated with other rock mainly phyllite and soil. Therefore, 10% of the associated materials was subtracted from the cross-sectional area (Table 3). After, area of cross-section M, K, H computation, the average distance between cross-section line AB and CD i.e. d₁ was measured by taking three measurement and the average distance between CD and EF i.e. d₂ was measured similarly. And finally, the volume was computed (Table 4) by the end area cross-sectional formula (Kumar, 1988).

\(\begin{align}V_{1}=d_{1} \times \frac{\text { Area of } C S(M)+\text { Area of } C S(K)}{2}, V_{2}=d_{2} \times \frac{\text { Area of } C S(K)+\text { Area of } C S(H)}{2}\end{align}\)       (1)

Fig. 5. Geological cross-section along the line A (NE)-B (SW), C (NE)-D (SW), and E (NE)-F (SW) respectively.

Table 3. Calculation for actual area occupied by quartzite

Table 4. Resource estimation from cross-sectional method

After getting total volume, volume was multiplied by the specific gravity of quartzite i.e. 2.65 to get total quartzite tonnage. This tonnage was multiplied by average grade of silica i.e. 95%, to get total silica tonnage.

Hence the total measured and proved gross reserve of silica present in the Naudanda Quartzite is about 2.6 billion ton.

Discussion

The main purpose of the study was to find the best silica resource for mining and ultimately to make country rich. For this, purpose prospecting of silica of the Naudanda Quartzite is very necessary as the Naudanda Quartzite is quite potential for high silica concentration. Medium grain, thick to medium bedded white to pale white quartzite is the main lithology of the Naudanda Quartzite. The average silica concentration of the area is more than 95%, having a good thickness about 700 m. As Naudanda Quartzite contains alternating beds of quartzite and phyllite in the upper part so from this portion good dimension stone can be extracted. In this area Sataun Daraun Dhunga Udhyog Pvt. Ltd. a mining company is extracting the slab stone from quartzite (Hirayama et al., 1988), had tested some samples of the Naudanda Quartzite and get, 91.66%, 97.11%, 94.22% or about 94.33% of average silica concentration which is 0.788% less than the result came from this study but indicates high percentage of silica. Only 5~6% other minerals are present in the quartzite so it can be processed to get 100% silica concentration. The Karra Khola is one of the popular places where high concentration of silica sand is found (DMG, 2004). Pun (2023) have tested silica concentration by gravimetric from four different locations; the Agrathe Khahare, the Khahare, the Chisapani Khahare and the Gauritar Khahare of the Karra Khola area. They found that the silica concentration was 94%. Comparing this result with the result of the Naudanda Quartzite is quite impressive as the concentration is 95.12%. Also, Sharma and Tamrakar (2023) have conduct strength and durability test for the Fagfog Quartzite for railway track ballasts in which they found significant potential for the material because of containing high amount of silica in the rock, as it can be correlated with the Naudanda Quartzite and can be concluded that the silica present in the Naudanda Quartzite is significantly high. Hence, the Naudanda Quartzite is rich in silica concentration and processing can be done to get 100% silica.

Conclusion

The main conclusion of the research can be presented as the given list:

(1) Recrystallization of quartz in the grain boundary and slightly elongated quartz grain indicates the quartzite of the Naudanda Quartzite has formed in low to medium grade metamorphism.

(2) Few amounts of detrital biotite, biotite, muscovite, sericite, feldspar, ferruginous oxide, magnetite, goethite, chert and dominantly quartz are the main minerals of the Naudanda Quartzite.

(3) The average silica concentration from petrographical analysis is 95.86% and from the chemical analysis is 95.12% which falls around grade 3 glass making silica sand category according to (IS 488, 1992).

(4) Silica present in the Naudanda Quartzite is economical and can be gone through further exploration.

(5) Gross estimated resources of proved and measured silica resource are 2.6 billion ton.