Hello I bought Vale and BHP Billiton, but reading this article quoting Goldman Sachs on copper has me worried, could you please comment? May it is too early to buy miners? : 

Eoin Treacy's view

Thank you for this question which may be of interest to other subscribers. The article you attached appears to assume there will be a property and investment crash in China. This is still an open question but it seems reasonably clear that infrastructure investment is not going to just stop. Recently announced easing measures suggest the Chinese administration is well aware of the risks. 

A potentially more important consideration is that the demand growth forecasts used by mining companies to justify major expansion projects have not panned out. The economics of mining means that a new mine, once commissioned, needs to continue to produce in order to generate cash regardless of the price currently on offer. This has led to miners abandoning new plans but completing late stage developments and increasing supply in order to try to drive higher cost producers out of business. This has been particularly poignant in the iron-ore market.  Copper is important but is less of a factor for either BHP Billiton or VALE. 

Nevertheless, copper is at an interesting juncture. It has been ranging with a downward bias for more than two years and has returned to test the psychological $3 area. If the more bearish prognostications are to prove credible it will need to sustain a break below that level. . 

BHP Billiton and VALE have competitive valuations but broke downwards from lengthy ranges in the last month to extend their declines. Breaks in progressions of lower rally highs will be required to signal a return to demand dominance. Some signal that they are willing to support iron-ore prices would likely be positive for their shares.