Following another strong showing today, the shares of iron ore miner Atlas Iron Limited (ASX: AGO) have now climbed a whopping 40% in the last five trading sessions.

The reason that Atlas Iron’s shares have skyrocketed all comes down to the remarkable increase in iron ore prices during the last month.

Much to the delight of the shareholders of Atlas Iron, Fortescue Metals Group Limited (ASX: FMG), and BHP Billiton Limited (ASX: BHP), iron ore prices hit a new six-month high of US$63.80 a tonne this week according to the Steel Index.

This meant the iron ore price defied the odds and rose by an incredible 15% during the month of October.

Which certainly comes as a huge surprise to an iron ore bear like myself. The forecast increase in supply from Australian and Brazilian producers had been expected to weigh heavily on prices in the final quarter.

But at present things look to be going the other way and iron ore prices show no signs of slowing.

Whilst I’m not about to change my mind and become bullish on iron ore just yet, I will happily admit that prices at this level do make the iron ore miners attractive investment options.

I’m not sure I would rush into an investment in Atlas Iron though. Whilst its cash costs (C1) are coming down, they are still over double the C1 costs that low-cost iron ore miner Fortescue Metals enjoys.

In FY 2017 Fortescue Metals expects average C1 costs to be US$12 to US$13 per wet metric tonne, whereas Atlas Iron has forecast for C1 costs in the region of US$25.50 to US$27 per wet metric tonne by my calculations.

If iron ore prices remain high then Fortescue Metals should continue to deliver bumper profits and pay down debt. For this reason I would recommend anyone bullish on iron ore to invest in Fortescue Metals ahead of Atlas Iron.

Alternatively, investing in these growth shares may be an even better option. Each has rapidly growing earnings and isn't dependant on commodity prices for growth.

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Motley Fool contributor James Mickleboro has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.