What: Shares of Freeport-McMoRan (NYSE:FCX) continued sliding again today, with the copper and oil producer down nearly 10% by 3:00 p.m. ET. The stock is now down 42.2% since trading for the year started just last week.

So what: We can blame today's sell-off on the continuation of global economic jitters due to concerns about further weakness in China's economy. These worries pushed the market down by more than 2% today and also put more pressure on commodity prices, which have a big impact on Freeport-McMoRan's cash flow. While the price of copper was only down a penny today, it is now trading at $1.95 per pound, which is a six-year low. Meanwhile, the global crude oil benchmark price fell more than 2.5% and, at one point today, it broke below $30 per barrel for the first time since 2004.

Those two commodity prices are important to Freeport-McMoRan because of the direct impact on its cash flow. In fact, over the course of a year, a $0.10-per-pound change in the price of copper is worth $320 million in cash flow for the company while every $5-per-barrel change in the price of oil equates to $170 million in cash flow. At current prices, copper is now $0.05 per pound below the company's 2016 plan while oil is $15 per barrel below plan. This weakness has the potential to jeopardize the company's ability to generate a sufficient amount of cash flow to both fund its capex plan as well as provide it with some excess cash flow to begin to pay down some of its enormous debt load.

Now what: Freeport-McMoRan needs to see copper and oil prices improve given how important both are to its cash flow. If both remain at current levels, it will negate the company's ability to generate any excess cash flow. That's a big concern because its debt load is already unsustainable at current commodity prices, so it can't afford to add any more debt to its balance sheet.