I have been working all day on the a mechanical trading system for GDX, it uses an indicator in Stockcharts.com, BPGDM.  I have made a modification to which improves it dramatically.  Also a big key to the system is taking the trigger on the day the BPGDM gives a buy or sell signal, not the next day like everyone has been doing.  

As you know, the BPGDM (and all bullish percent indexes) do not update until 1.5 hrs after the market closes.  This has always been a problem with the bullish percent indexes and why the majority of people can only use the buy/signals for the next day (because the market is already closed when the indicator updates).

 HOWEVER I figured out how to update the BPGDM intra day and get the signal before the close, that's a BPT secret.  Therefore, taking the trade on the daily of the BPGDM buy/sell signal dramatically improves the system.  Also selling any longs when the BPGDM is at 83.5% or higher also improves the system quite a bit.

Below I've posted a video overview as well as some detailed statistic

Here's a video overview:  Click here!