What is the test for making a discovery in a mining claim?

The principal objection made to the charge on this branch of the case is that the court instructed the jury that the mineral discovered must, in order to constitute a discovery, be of such quantity and character and found under such circumstances as to justify a man of ordinary prudence in the expenditure of his time and money in the development of the property. It is argued that a discovery sufficient to justify the expenditure of time and money in the development of a mining claim must necessarily be greater than that which is necessary to justify the expenditure of money for the purpose of exploration, with the reasonable expectation that, when developed, the claim will be found valuable as a placer mining claim. Counsel for the plaintiffs in error have assumed for the word 'development' a broader meaning than was intended in the charge. The court did not mean that, in order to comply with the law, there must be such a discovery as to justify the expenditure of time and money upon a claim to the extent of opening up the whole thereof and acquiring an exhaustive knowledge concerning its resources. The word as it was used by the court, and as in connection with the whole charge it must have been understood by the jury, was equivalent to the word 'exploration,' and was used in the sense in which it was employed in Chrisman v. Miller, 197 U.S. 313, 323, 25 Sup.Ct. 468, 470, 49 L.Ed. 770, in which the court thus quoted with approval the language of Mr. Justice Field in a prior case: