牡丹溪曾經盛產砂金，砂金來自於上游牡丹山黃金礦脈，經過雨水滲入山體，地下水融解礦脈帶出金粒，最後沉積在牡丹溪的河床上。日治時期曾掀起淘金熱潮，吸引大量民眾到此淘洗，砂金鑛權分為三段，第一段牡丹溪上游大約政光一號橋以北為武丹坑金鑛所有，第二段牡丹溪中游政光一號橋以下至聖南寺附近河段，由小河俊藏開採，第三段牡丹溪中游至魚行附近雙溪河道，礦名雙溪砂金，與武丹坑金鑛相同之礦主所經營。其中靠近牡丹國小的第二段砂金設權開採期間約為1910至1916年。

Mudan River was once rich in placer gold. The gold came from the veins in Mudan Mountain upstream. Rainwater seeped into the mountain, dissolving the gold and carrying gold particles down to the riverbed. During the Japanese ruling period, a gold rush attracted many people to the area to pan for gold. The mining rights were split into three sections. The first section, upstream north of Cheng-Kuang No. 1 Bridge, belonged to Wudankeng Coal Mine. The second section, from below Cheng-Kuang No. 1 Bridge to near Shengnan Temple, was mined by Koga Shunnzou. The third section, from midstream Mudan River to Shuangxi River near the fish market, was called Shuangxi Placer Gold and was run by the same owner as Wudankeng Coal Mine. Among the three sections, the second section, near Mudan Elementary School, had mining rights from around 1910 to 1916.