Keep it simple, Fool!

Sure, you could reinvent the wheel. You could pore through the vast universe of precious-metal equities to craft your own individual formula for success. That's what I did, though it took me years of exhaustive research and constant tweaking to hone my own approach.

I'm here to tell you that it doesn't have to be that hard. As I scrutinize the holdings of the exchange-traded funds (ETFs) that gold and silver investors now have at their disposal, I am struck by the degree to which Fools can achieve a roughly similar exposure to my own with just a few ETF holdings (and one closed-end fund).

This is not a one-size-fits-all investment formula for exposure to gold and silver. The four holdings below represent, in my opinion, the easiest way to gain comprehensive access to this booming sector. Keep in mind this is merely a template, and a rather aggressive, growth-focused one at that. As such, allocations must be adjusted as needed to meet one's own particular investment objectives. Decisions regarding total allocation to gold and silver are left for the individual to render independently.

Global X Gold Explorers ETF (NYSE: GLDX)
Launched earlier this month, GLDX places the final piece into the puzzle that makes this all-ETF approach such an attractive option. Top holdings feature explorers that have already made significant gold discoveries, which removes a key risk factor from the group. Headliners include comeback sensation NovaGold Resources, Fronteer Gold (with its highly prospective Long Canyon project), and Rubicon Minerals (AMEX: RBY) (which just unveiled a 4-million-ounce inferred gold resource at its Phoenix Gold project in Ontario). The ride for this ETF likely won't resemble a straight line, by any means, but I believe the fund offers unparalleled one-stop potential to profit from the ongoing precious-metals bull market.

Global X Silver Miners ETF (NYSE: SIL)
When this ETF hit the market earlier this year, I expressed my unwavering confidence in the fund's performance by predicting it would outperform the S&P 500 by 200% within the course of five years. My Motley Fool CAPS pick has outperformed the index by more than 50% this far, and I believe the ETF's top stocks like Silver Wheaton (NYSE: SLW), Pan American Silver, and Hecla Mining will ensure continued success. Smaller holdings in names like Endeavour Silver, Great Panther Silver, and Alexco Resource, meanwhile, offer some truly epic upside exposure, by this Fool's estimation.

Market Vectors Gold Miners ETF (NYSE: GDX)
The GDX is dominated by widely recognized titans of the gold mining industry, including Barrick Gold, Goldcorp, and Newmont Mining. Silver Wheaton is duplicated in this ETF (see above), but if there's one stock to double up on in the group, that's the one! High-quality intermediate miners like Agnico-Eagle Mines and Yamana Gold (NYSE: AUY) are also well-represented within the fund.

Central Fund of Canada (AMEX: CEF)
Some exposure to physical bullion is recommended within any well-balanced approach to precious-metals investment. Although complex tax considerations may apply, I view CEF as the ideal bullion proxy. The fund has been around since 1961, and offers roughly equal exposure to "unencumbered" gold and silver bullion. Because units routinely trade at a premium to net asset value, the fund's periodic, non-dilutive unit offerings may provide the most opportune entry points.

Seasoned precious-metals investors may note the absence of the Market Vectors Junior Gold Miners ETF within my proposed formula. I omitted the fund due to the degree of overlap between its holdings and those of the first two funds above. Suffice to say, I believe that it, too, will launch with the rocket that is this ongoing secular bull market for silver and gold.

I understand that not all prospective precious-metals investors will wish to hold four separate vehicles to obtain their exposure. For those determined to hold only one of these funds, I believe that the silver miners ETF is the must-have cream of the crop. I personally do not own shares, but only because I own the majority of its holdings individually.

This article is not intended to extinguish the need for investors to conduct their own ample and constant due diligence. After all, acquiring exposure to precious metals could provide no benefit at all if one can't stomach the gut-wrenching volatility these metals and their related equities will likely continue to experience in the months and years to come.

I am eager to hear from seasoned and newcomer precious-metals investors alike and I urge those who have crafted their own individual strategies for investing in the space to share their formulae in the comments section below. The above is certainly not the only formula one could follow, and I won't even claim it's the best. It is merely the simplest means I could identify to achieve an approach that's qualitatively similar to my own.