What intensified british interest in south africa in second half of the nineteenth century?

The discovery of diamonds and gold as valuable resources to be mined in South Africa.

Diamonds were discovered in South Africa in the 1860s, and gold was found in the 1880s.  White settlements in South Africa prior to that were mostly agricultural, but the "mineral revolution" caused huge changes to imperialistic interest in the region and sparked the building of railroads and urbanization, as well as intensifying conflict between European white people and the native black people in South Africa.

C.east asiais the answer.