Market Vectors Junior Gold Miners ETF (NYSEArca: GDXJ) is on track for a roughly 30% gain in the third quarter with the small-cap miner fund pulling away from bullion prices since the beginning of August.

GDXJ is also outperforming its large-cap peer, Market Vectors Gold Miners ETF (NYSEArca: GDX), which is up about 20% the past three months. The largest bullion-backed ETF, SPDR Gold Shares (NYSEArca: GLD), has gained about 13%.

Paul Weisbruch, head of ETF and options trading at Street One Financial, notes that options traders have been using GDX call options to take a bullish stance on gold-related stocks. [ETF Chart of the Day: Gold Miners]

Just in September, investors have added $306.7 million to GDX and $181.9 million to the small-cap GDXJ, according to IndexUniverse ETF flow data. Investors have been piling into gold and miner ETFs on central bank stimulus. [Investors Add Nearly $3B to Gold ETFs in September]

Christian Magoon at notes that GDX has outperformed mighty Apple (NasdaqGS: AAPL) by nearly 10 percentage points over the last month.