It’s been a dark day for Australian investors with the S&P/ASX 200 (Index: ^AXJO) (ASX: XJO) collapsing after the briefest of relief rallies, yet there is a slither of light coming from one of the most unexpected sources.

They were the laggards of the local share market in 2015, and have been so far in 2016 as well, but the country’s biggest miners are bucking the downward trend today and providing some much-needed support for the broader market.

Shares of BHP Billiton Limited (ASX: BHP) have risen 1.1% today, while South32 Ltd (ASX: S32) shares have risen 2.2% as well.

Considering BHP shares fell to their lowest level in more than a decade this morning and South32’s shares are languishing near the lowest price in the company’s short history, could today’s gains reflect that now is the time to jump on board with the miners?

Should you buy?

The share prices of both miners have been absolutely crushed in recent times due to fears of a slowing global economy, driven by waning Chinese growth, which has resulted in plunging commodity prices.

BHP has mostly been impacted by the sharp fall in iron ore and oil prices, but coal and copper are also under pressure. South32 has also been hurt by the falling coal prices, together with the declines experienced in the aluminium and manganese markets.

By conventional standards, shares of both companies look cheap. BHP Billiton, for instance, trades on a trailing 11.3% fully franked dividend yield and with a price-book ratio of roughly 0.9x, according to data from Capital IQ. South32’s shares are trading on an even lower price-book ratio of roughly 0.3x.

In other words, you could buy shares in either company right now for less than the net value of their assets.

However, it should be noted that these figures are based on balance sheet figures provided by the companies at their most recent earnings reports. Conditions in the resources sector have deteriorated considerably since then. The price of iron ore, for instance, has fallen nearly 11% since last Tuesday while oil prices have also plunged to around US$30 a barrel. Both commodities, amongst others, are tipped to fall even further over the coming months.

Indeed, this will have an impact on the earnings results of both miners which could be forced to review the value of their assets, leading to impairments. That is likely why investors are attributing such a heavy discount to the shares right now.

Shares of BHP and South32 both look cheap, but they’re cheap for a reason. With conditions in China continuing to worsen and commodity prices expected to continue falling, it is my opinion that neither are particularly safe places for your money right now, and you’d be best to avoid them in favour of other bargain companies.

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Motley Fool contributor Ryan Newman has no position in any stocks mentioned. Unless otherwise noted, the author does not have a position in any stocks mentioned by the author in the comments below. You can follow Ryan on Twitter @ASXvalueinvest.

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.