Copper ore is heated in a blast furnace after mixing with silica to extract copper. During this process, several reactions occur which result in the production of copper in the form of copper matte.

1. Reaction between Copper Ore and Silica:
The copper ore, which usually contains copper sulfide, is mixed with silica (SiO2) in the blast furnace. The silica acts as a flux, helping to remove impurities and facilitating the formation of slag. The main reaction that takes place is:

CuFeS2 + 2SiO2 → Cu2S + 2FeSiO3

In this reaction, copper sulfide (CuFeS2) reacts with silica to form copper(I) sulfide (Cu2S) and iron silicate (FeSiO3). The iron silicate is the slag that is formed and separates from the molten copper.

2. Formation of Copper Matte:
The copper(I) sulfide (Cu2S) produced in the previous reaction is further heated in the blast furnace. At high temperatures, the copper(I) sulfide reacts with more copper(I) sulfide to form copper(I) matte, which is a mixture of copper(I) sulfide and some copper(I) oxide:

2Cu2S + O2 → 2Cu2O + 2SO2
3Cu2S + 2Cu2O → 6Cu2S + SO2

The copper matte is a black, brittle material that contains a high concentration of copper. It is tapped from the blast furnace and further processed to obtain pure copper.

3. Conversion to Copper Metal:
The copper matte is then subjected to a process called smelting, where it is heated in the presence of oxygen. The oxygen reacts with the impurities in the matte, such as iron and sulfur, to form slag. The remaining copper is then further refined to remove any remaining impurities and obtain pure copper metal.

In summary, when copper ore is heated in a blast furnace after mixing with silica, the iron oxide slags off as iron silicate, and copper is produced in the form of copper matte. This copper matte is then processed to obtain pure copper metal.