The FTSE 100 is home to the largest companies on the London Stock Exchange, many of which are doing business all over the globe. And with industries such as banking, mining, and healthcare thriving in recent years, the UK’s flagship index has delivered some stellar performances thanks to its concentration in these sectors.

By investing in these industry titans, a portfolio automatically benefits from a variety of advantages, including proven business models and substantial economies of scale.

Over the long term, having this upper edge can help deliver some robust gains for investors. So with that in mind, let’s explore how someone with £5,000 can start building wealth with the FTSE 100.

Diversified passive growth

One of the easiest ways to invest in the FTSE 100 is with a low-cost index tracker. Within a single transaction, a portfolio becomes instantly diversified across all 100 of the UK’s large-cap companies, granting some level of exposure to almost every industry.

Historically, investors following this strategy have earned an average of around 8% a year. But as previously mentioned, 2025 was an exceptional year. And investors went on to earn a chunky 26.1% total gain, transforming £5,000 into roughly £63,05 in just 12 months!

Maximising returns

Last year’s 26.1% total return for index investors was impressive. But it pales in comparison to what some stock pickers achieved in the same time frame.

Take Fresnillo (LSE:FRES) as a perfect FTSE 100 example to consider. The Mexican gold and silver miner was perfectly positioned to capitalise on the enormous tailwinds driving up demand for precious metals.

Higher inflation paired with rising geopolitical tensions enabled the group’s revenue to charge ahead by 30.5% in 2025. But since operating expenses remained largely fixed, the group was able to exercise exceptional operating leverage. And consequently, total net income skyrocketed by 594.3% from $226.7m to $1.6bn!

With that in mind, it’s no wonder the share price erupted by more than 430%, transforming £5,000 into over £26,500. And that’s before counting dividends!

Still worth considering

With demand for precious metals remaining strong in 2026, the price of gold has continued to climb, with silver remaining largely stable at elevated levels. And with both commodities continuing to trade at record high levels, Fresnillo looks once again primed to deliver some powerful profits in 2026.

However, whether that will translate into further explosive share price gains isn’t guaranteed. Why? Because these growth expectations may already be baked into the share price. And even if gold and silver prices continue to climb, Fresnillo’s production volumes have actually been steadily suffering as a result of falling ore grades at its mines.

With management investing heavily in late-stage exploration projects as well as executing international acquisitions, production volumes are expected to eventually get back on track. But whether or not precious metal prices will still be elevated by then is the main risk investors need to carefully consider.

Overall, I’m not convinced that Fresnillo will be another four-bagger for investors in 2026. But it goes to show that by investing in the right ones, stock pickers can achieve jaw-dropping returns that leave passive index investors in the dust.