a heart of gold
形容一個人真誠、善良的本性
*Sarah always goes out of her way to help everyone she can—she really has a heart of gold. 莎拉總是盡心盡力地幫助每個人，她真的非常善良。

gold mine of information
形容擁有豐富知識的人或物
*Grandfather is a gold mine of information about World War I.祖父了解非常多關於一次世界大戰的知識。

(as) good as gold
1.「像黃金一樣好」，形容聽話又乖巧的樣子
*Sure, I'll baby-sit Cindy's kids tonight—they're as good as gold every time I watch them.好，今晚我會照顧Cindy的孩子，我每次照顧他們，他們都聽話又乖巧。
2. 也形容貨真價實、合法的
*According to the curator, this painting is as good as gold.根據策展人的說法，這幅畫是真跡。

sitting on a gold mine
「坐在金礦上」，是形容手上操控著某種很有價值的東西，或很有潛在價值的東西
*When I found out how much the old book was worth, I realized that I was sitting on a gold mine.當我發現這些舊書價值多少錢時，我才意識到我手中掌握了多少財富。

worth its/(one's) weight in gold
形容非常高價值、重要、有用的
*When you're in a foreign country, you'll find that a translator is worth his weight in gold.當你在國外的時候，你會發現翻譯有多麼地重要。

pot of gold
形容特別龐大的一筆錢，或高價值的資源
*You're not going to find a pot of gold going into this business, but it's definitely lucrative enough to make a living.你在這一行賺不到一大桶金，但絕對足以維持生活。

black gold
我們常說的「黑金」(不是黑道那個...)就是指又黑又值錢的石油囉
*We were barely surviving until Jed discovered black gold beneath our field, and now we're richer than we could ever imagine! 我們當時幾乎活不下去，後來傑德在我們的土地上發現石油，現在我們的富有程度超乎我們的想像！

there's gold in them there hills
形容一項投資中有潛在的巨大利益
*With the rise of smartphones, the lucrative market of mobile apps came to the fore, and developers around the world realized that there's gold in them there hills. 隨著智慧型手機崛起，利潤豐厚的行動應用程式市場備受矚目，全世界的開發人員都意識到其中有龐大的潛在利益。

資料來源：網路、字典、名揚翻譯