It came as the firm released results from 87 samples completed last month.
Particularly, ECR was trying to confirm whether bulk sampling or small scale test mining, would be appropriate at the prospect in La Rioja province.
"Although some high grades were recorded, the results of the programme, in combination with data from previous sampling and drilling, are inconclusive," the firm said in a statement.
"Further exploration will be necessary to acquire a complete understanding of the complexities of the mineralisation at El Abra.
"In particular, given the irregular and discontinuous nature of the veins and erratic grade distribution, it will be difficult to calculate a resource at El Abra without bulk sampling of the vein to fully understand its grade and potential."
Two samples - one from underground and one from surface - were sent for assay and showed grades of 27.8 g/t gold and 31.9 g/t gold with 69% and 64% of the yellow metal reporting to the coarse fraction.
This indicates that a signiﬁcant percentage of gold at El Abra occurs as coarse ﬂecks and conﬁrms that large sample sizes and specific methodology would be required to provide the most representative assay results.
Shares fell around six per cent, to stand at 0.39 pence.
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