Which geological feature is associated with ruby deposits in Thailand and Cambodia?

The correct answer is alkali-basalt, as it is the geological feature most commonly associated with ruby deposits in Thailand and Cambodia. Rubies typically originate from metamorphic rocks, and in this region, the specific geological processes involve the alteration of mineral-rich volcanic rocks, including alkali-basalt. These materials are conducive to the formation of corundum, the mineral that crystallizes into rubies.

In contrast, granite, sandstone, and limestone do not provide the right conditions for ruby formation in these regions. Granite is an igneous rock that can be associated with other types of gem deposits, but not specifically with rubies. Sandstone and limestone are sedimentary rocks that lack the necessary conditions for the formation of corundum. Thus, alkali-basalt is specifically noted for its correlation with the genesis of ruby deposits in the context of the local geology of Thailand and Cambodia.