Before looking at some individual mining prospects, a word about GDX: Consider that NEM and GOLD comprise 21.8% of GDX. These two companies both purchased rival companies is 2019: In January, GOLD acquired Randgold, a $6.5b deal, and in April, NEM purchased its top rival, Goldcorp, for $10b.
If invested in GDX, keep tabs on exploration costs and production of NEM and GOLD to monitor their strength. It is an increasing challenge for them to find new gold to mine economically at the scale and pace their size demands.
If you insist on an ETF to trade the gold miners, then consider GDXJ instead of GDX, as mid-tier and junior gold mining stocks may outperform the large miners.
For mining prospects beyond GDX and GDXJ, one can make their own basket of royalty and mining production companies that will likely outperform. The smaller minershave lower market caps and smaller capital inflows.
Royalty/streaming companies help fund exploration and production projects, in exchange for a royalty on future production. They are specialized financiers, sans the hard work of operating a mine. Royalty and streaming stocks have substantially lower costs and greater margins, are well diversified with less exposure to risk, and some pay a dividend.
SLW is the largest precious metal streaming company in the world. FNV and RGLD are two other large players. Franco-Nevada has streams from Barrick Gold, Goldcorp, Agnico Eagle, SSR Mining, Newmont Mining, Yamana Gold, Hecla Mining, Sibanye Gold, Coeur Mining, Pan American Silver, Kinross Gold, Kirkland Lake…and many more.
These charts [and others] are in my SlopeCharts watchlist, SharedMiners which are accessible to Gold and Diamond members via the shared watchlist feature.