金矿 means "gold mine" and refers to a mine where gold is extracted. It combines 金 (gold) with 矿 (mine/ore). It is used in both literal mining contexts and occasionally figuratively to describe a lucrative opportunity.
这座山里发现了一个大型金矿。
zhè zuò shān lǐ fāxiànle yīgè dàxíng jīnkuàng.
A large gold mine was discovered in this mountain.
他在澳大利亚的金矿工作了五年。
Tā zài Àodàlìyà de jīnkuàng gōngzuòle wǔ nián.
He worked in a gold mine in Australia for five years.
对投资者来说,这个行业简直就是一座金矿。
Duì tóuzīzhě lái shuō, zhège hángyè jiǎnzhí jiùshì yī zuò jīnkuàng.
For investors, this industry is simply a gold mine.