HI Albert,
This is a really good question and one I looked into for a client recently using data for the Market Vectors ETF since 1998.
The analysis can be found [broken link removed]
The conclusion reached is that mining stocks are a poor proxy for the spot price of gold and do not represent an "asset class" or specifically a section of the equity market with its own risk/return characteristics.
This conclusion is further supported by [broken link removed]which looks at US Mining companies since 1926.
Again,mining stocks consistently underperform the S&P 500 since 1926 with just a brief period of outperformance in the late 1970s early 80s when the spot price of gold and other commodities shot up.
Overall, there are better ways to buy gold -such as actually buying gold and better ways of taking positions in equities.
Regards
Marc