The text specifies that extensive deposits of high-grade Silica Sand occur near Shankargarh and Bargarh in Allahabad district. Silica sand is an essential source of glass sand, and the quality of the sand in Naini area of Allahabad is particularly high.

Introduction:
The district in Uttar Pradesh that contains extensive deposits of high-grade Silica Sand is Allahabad. Silica sand is a type of sand that contains high levels of silica, which is a mineral composed of silicon dioxide. It is widely used in various industries, including glass manufacturing, foundries, construction, ceramics, and chemical production.

Reasons for choosing Allahabad:
There are several reasons why Allahabad is known for its extensive deposits of high-grade Silica Sand:

Geological factors:
1. Presence of alluvial deposits: Allahabad is located in the Gangetic Plain, which is known for its alluvial soil. Alluvial deposits are formed by the action of rivers and contain a variety of minerals, including silica sand.
2. Proximity to the riverbed: Allahabad is situated near the confluence of the Ganges and Yamuna rivers. The riverbeds of these rivers often contain rich deposits of silica sand. The continuous erosion and deposition of sediment by these rivers contribute to the availability of high-grade silica sand in the region.

Economic significance:
1. Demand from industries: Silica sand is a crucial raw material for various industries, including glass manufacturing, foundries, and ceramics. The presence of extensive deposits of high-grade silica sand in Allahabad makes it an economically significant district.
2. Infrastructure and transportation: Allahabad has well-developed infrastructure and transportation networks, which facilitate the extraction and transportation of silica sand. This makes it easier for industries to access the silica sand deposits in the district.

Other factors:
1. Mining activities: Allahabad has a history of mining activities, including the extraction of minerals like silica sand. This has led to the identification and exploitation of extensive deposits of high-grade silica sand in the district.
2. Government initiatives: The Uttar Pradesh government has taken initiatives to promote mining activities in the state. This has encouraged the exploration and extraction of silica sand in Allahabad, thereby making it a district with extensive deposits of high-grade silica sand.

Conclusion:
Allahabad district in Uttar Pradesh is known for its extensive deposits of high-grade silica sand. The geological factors, economic significance, and other factors discussed above contribute to the presence of these deposits in the district. The availability of high-grade silica sand in Allahabad makes it an important resource for various industries, further contributing to the economic development of the region.